P2 revision pack

Physics Unit P2 ‘Physics for Your Future’ Study and Revision Pack (Higher Paper)

Content P2 overview and assessment tracking Formulae sheet P2.1 Specification statements P2.1 Exam Questions P2.2 Specification statements P2.2 Exam Questions P2.3 Specification statements P2.3 Exam Questions P2.4 Specification statements P2.4 Exam Questions P2.5 Specification statements P2.5 Exam Questions P2.6 Specification statements P2.6 Exam Questions

Revision tips in appendix

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Name: __________________________________ Class: __________________________________

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P2 Overview

Overview and assessment tracking Please use the table below to keep track of your revision. The smarter you work the better results.

Revision Questions Marks % in Marks in % in complete? completed? in first first try second second try try try

P2.1

P2.2

P2.3

P2.4

P2.5

P2.6

Use the grade boundaries below as a guide to the grade you are achieving:

% 90 80 70 60 50 <50

Grade A* A B C D U

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Topic 1 – Static and current electricity

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STATIC ELECTRICITY Static electricity is caused by an electrical (‘electrostatic’) charge building up on insulating materials – including on you All atoms contain electrically charged particles called protons and electrons: o Protons have a positive charge and are found in the nucleus of atoms o Electrons move around the outside of the atom at different distances from the nucleus – they are negatively charged o The positive charges on the protons are balanced by the negative charges on the electronsàatoms have no overall charge Note: the nucleus also contains neutrons, which have no charge Generating static electricity: When two insulating materials are rubbed together, friction is generated and electrons may be transferred from one material to the other (note: protons can’t be transferred because they are fixed in the nuclei of atoms): o The material gaining electrons now has more electrons than protonsàhas a negative charge o The material losing electrons now has more protons than electronsàhas an equal positive charge Objects charged with static electricity can attract or repel each other: o If the charges on the two objects are different, they will attract each other o If the charges are the same as each other (i.e both positive or both negative), the objects repel If you rub a balloon on a jumper you can get it to stick to a wall – this process is called charging ‘by induction’ and the charge produced is an induced charge…

Explanation for this: o When the balloon is rubbed against the jumper, electrons are transferred from the jumper to the balloonàthe balloon becomes negatively charged o When the balloon is placed against the wall, the electrons in the wall are repelled by the balloon’s negative charge and move away o The positive charge left behind on the wall (the ‘induced charge’) attracts the negative charge on the balloonàthe balloon sticks to the wall Why it’s difficult to charge a conducting material with static electricity: Insulating materials (e.g a polythene rod) do not conduct electricity…: o àelectrons that are transferred cannot move through the material – i.e they stay close together at the end of the polythene rod o àstatic charge builds up at the end of the polythene rod Conducting materials (e.g a metal rod) conduct electricity…: o àelectrons that are transferred spread themselves out through the metal rod o àthe extra static charge is difficult to detect This is why static electricity builds up between insulating materials and not between conducting materials USES AND DANGERS OF STATIC ELECTRICITY Shocks from everyday objects: You can sometimes build up an electrostatic charge just by walking on a carpet: o As the shoes rub along the carpet, electrons are transferred from the carpet to the personàperson becomes negatively charged o If the person then touches a conducting material (e.g metal object), the person feels a small electric shock as electrons flow from the person, through the metal object to the earth o The direction in which electrons flow depends on the charge of the object: § for a negatively charged object (as in this example), electrons flow from the earth to the object § for a positively charged object, electrons flow from the earth to the object The process of electrons flowing from a person to the ground through an object, or the other way around, is called ‘earthing’ After earthing, the person is discharged (i.e no longer has an electrostatic charge) Lightning: 4

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Large charges of static electricity can build up on clouds, causing electrons to flow through the atmosphere between the clouds and the ground (electrons can flow in either direction…i.e from ground to clouds or from clouds to ground) This produces the huge spark that we see as lightning Overcoming the dangers of electrostatic charges: To reduce the dangers of the build-­‐up of static electricity… o there needs to be a path between the object with electrostatic charge and the ground, through which electrons can flow… § for electrons to flow along it, the ‘path’ must be made of a material that conducts electricity…àin most cases, it’s made of metal o This earthing process discharges the object and prevents sparks being produced E.g refuelling aircraft: o As fuel flows through a refuelling pipe, static electricity can build up o The aircraft can also build up a static charge as it flies through the air o àa bonding line (a metal wire) is used to connect the aircraft to the earth before it is refuelled o This discharges the aircraft of any electrostatic charge that may have built upàno sparks are produced A similar problem can occur when tankers deliver fuel to filling stations: o In this case, the hose used to fill the underground fuel tanks is made of a conducting materialàno sparks are produced Uses of static electricity: Static electricity can be useful…

E.g it can be used in electrostatic spray painting to make the spray spread out…: o The metal spray nozzle is connected to the positive terminal of an electricity supplyàdroplets of paint pick up a positive charge o The positively charged droplets repel each otheràspread out o The object to be painted is given a negative charge o àthe paint droplets are attracted to the surface of the object Note: static electricity is also used in insecticide sprayers ELECTRIC CURRENTS In conducting materials (e.g metals), some of the electrons from each atom are free to move about -­‐ this flow of electrons produces an electric current In a piece of metal, the free electrons all move round in different directions When a metal wire is placed in an electrical circuit (it must be a complete circuit), the cell (battery) pushes the free electrons in one direction around the circuit… o Cells and batteries supply current that flows in only one direction – this is called ‘direct current’ Generators produce ‘alternating current’ – i.e electrons change direction many times each second Charge and current: An electric current is the rate of flow of charged particles Units: o Charge – measured in coulombs (C) o Current – measured in amperes (or amps, A) The size of the electric current depends on how much charge is passing a point in a circuit each second: o à1 ampere is a flow of 1 coulomb of charge per second The equation linking charge and current: o charge (coulombs, C) = current (amps, A) x time (seconds, s) o Q = I x t o I.e the more charge that passes a point in a circuit per second, the greater the current E.g: o a current of 5A flows for 10s…how much charge has flowed through the circuit? o Charge = 5 x 10 = 50 C

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P2 Specification Physics for your future

Topic 1: Static and Current Electricity

Revised ü 1 2

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1.3 Be able to explain how the material gaining electrons

becomes negatively charged and the material losing electrons is left with an equal positive charge.

1.4 Know that like charges repel and unlike charges attract.

1.5 Be able to demonstrate an understanding of common electrostatic phenomena in terms of movement of electrons, including: a) shocks from everyday objects b) lightning c) attraction by induction such as a charged balloon attracted to a wall and a charged comb picking up small pieces of paper 1.6 Be able to explain how earthing removes excess charge by movement of electrons.

1.7 Be able to explain some of the uses of electrostatic charges in everyday situations, including paint and insecticide sprayers.

1.8 Be able to demonstrate an understanding of some of the dangers of electrostatic charges in everyday situations, including fuelling aircraft and tankers together with the use of earthing to prevent the build-­‐up of charge and danger arising.

1.9 Know that an electric current is the rate of flow of charge.

1.10 Know that the current in metals is a flow of electrons.

1.11 Be able to use the equation: charge (coulomb, C) = current (ampere, A) x time (second, s) Q = I x t 1.12 Know that cells and batteries supply direct current (d.c.).

1.13 Be able to demonstrate an understanding that direct current (d.c.) is movement of charge in one direction only.

1.1 Be able to describe the structure of the atom, limited to the position, mass and charge of protons, neutrons and electrons 1.2 Be able to explain how an insulator can be charged by friction, through the transfer of electrons.

RAG Current

Topic

P2.1 Specification statements

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P2.1 Exam Questions-­‐ 58 marks, 58 minutes.

Q1. (a) A lightning strike on a metal tower can be described as follows.

In the cloud.

A thunder cloud contains moving ice particles.

Some of these ice particles are negatively charged and some are positively charged.

The negatively charged particles move to the bottom of the cloud.

When the charged cloud is over the metal tower.

A charge builds up on the top of the metal tower as the cloud passes over.

During the lightning flash.

Eventually a flash of lightning travels between the cloud and the tower. (i) Which row of this table is correct when the cloud is over the top of the tower before the lightning flash?

Put a cross (

) in the box next to your answer.

(1)

A B C D

charge on top of the cloud is negative negative positive positive

charge on top of the tower is negative positive positive negative

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(ii) Here are four statements.

Three of these are a reason for what happens at each stage.

Choose the best reason for each of the stages listed below by writing its number in the box next to the description of what happens.

One has been done for you.

A reason can only be used once.

(2)

(iii) Explain what happens to the charge on the metal tower as a result of the lightning flash.

(2) .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. (b) During the lightning flash a total charge of 52 C flows.

The average current is 2600 A. Calculate the duration of the flash in seconds.

(3)

..............................................................................................................................................

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(c) When fuel tanks on an aircraft are being filled, the aircraft, fuel pipes and tanker are connected by a metal wire to the ground.

Explain why this greatly reduces the chance of a spark.

(2) .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. ..............................................................................................................................................

(Total for Question is 10 marks) Q2. (a) A student wins a trophy. It is a metal cup on a black plastic base.

The student cleans the trophy.

She holds one of the metal handles and rubs the rest of the trophy with a dry cloth. (i) Complete the sentence by putting a cross ( ) in the box next to your answer.

The plastic base becomes negatively charged because it gains (1) A B C D

atoms becquerel einstein radium

(ii) Explain why the base gains a negative charge when she rubs the trophy with the cloth.

(2) .............................................................................................................................................. .............................................................................................................................................. ..............................................................................................................................................

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(iii) The metal cup does not become charged when she rubs the trophy.

Suggest why the cup does not become charged.

(2) .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. (iv) Some dust particles in the air drift near to the plastic base just after she cleans the trophy.

Which diagram shows the correct distribution of charges on a dust particle near to the charged plastic base?

Put a cross (

) in the box next to your answer.

(1)

(b) Describe one situation where separation of electric charge can create a spark.

(2) .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. ..............................................................................................................................................

(Total for Question = 8 marks)

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Q3. Using static electricity Waste gases contain smoke particles.

The diagram shows how smoke particles can be removed from waste gases as they rise through a chimney.

(a) Complete the sentence by putting a cross ( ) in the box next to your answer.

When the smoke particles go through the metal grid they become negatively charged.

This is because they (1) A B C D

gain electrons gain protons lose electrons lose protons

(b) When the negatively charged smoke particles move up the chimney, they are attracted to the metal plates. (i) State why the metal plates attract the smoke particles.

(1) .............................................................................................................................................. ..............................................................................................................................................

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(ii) State what happens to the charge on the smoke particles when they reach the metal plate.

(1) .............................................................................................................................................. (c) There is a current of 1.4 A between the grid and the plates. (i) Calculate the charge transferred by this current in two minutes. State the unit.

(3) charge = ........................................ unit ........................................ (ii) The potential difference between the grid and the plate is 400 V. Calculate the electrical energy transferred in two minutes.

(2) energy transferred = ....................................... joules (Total for Question = 8 marks) Q4.

A battery sends a current through a metal wire. (a) (i) Complete the sentence by putting a cross (

) in the box next to your answer.

Direct current is movement of charge (1) A B C D

backwards and forwards in many directions in one direction up and down

(ii) Complete the sentence by putting a cross (

) in the box next to your answer.

The particles that flow in the metal wire are (1) A B C D

atoms electrons protons neutrons

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(b) The current in a wire is 3.7 A. Calculate the charge that flows into the wire in 13 s.

(2)

.............................................................................................................................................. (c) Plastic is an insulator.

A student rubs a piece of plastic with a cloth.

This gives the plastic a negative charge. (i) Explain how the plastic is charged by the rubbing.

(2) .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. (ii) The cloth is also charged when it rubs against the plastic.

Describe the charge on the cloth.

(2) .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. ..............................................................................................................................................

(Total for Question is 8 marks)

Q5. Electrostatic discharge (a) Marie works in an office which has a nylon carpet.

She walks across the carpet towards her filing cabinet.

There is friction between her shoes and the carpet.

When she touches the metal handle of her filing cabinet she feels an electric shock. (i) State the name of the charged particles which have been transferred between the carpet and her shoes.

(1) ..............................................................................................................................................

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(ii) The following sentences explain how Marie got the electric shock.

The sentences are in the wrong order.

Put them in the correct order by numbering the boxes.

Two have been done for you.

(2) actions

order in which the actions happen

Marie walks across the nylon carpet charge flows from Marie to the filing cabinet Marie touches the handle charge is transferred by friction on to Marie Marie has lost her negative charge a negative charge builds up on Marie

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(b) Marie has another filing cabinet which has a black conductive strip at the top.

This black strip helps to prevent electric shocks.

This strip has a high resistance but still conducts charge.

If Marie touches the strip before touching the handle she does not feel a shock.

Explain, using the idea of electric current, why Marie does not feel a shock.

(3) .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. ..............................................................................................................................................

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*(c) Sparks from electrostatic discharge can sometimes be very dangerous. They can cause a fire or an explosion.

Safety precautions are taken to reduce risks.

Explain how safety precautions, in a particular situation, reduce the risks of fire or explosion.

You may draw a labelled diagram to help with your answer.

(6) .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. ..............................................................................................................................................

(Total for Question = 12 marks)

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Q6. (a) Vicky combs her hair with a plastic hair comb.

The comb now has a negative charge. (i) Complete the sentence by putting a cross (

) in the box next to your answer.

The comb has a negative charge because it has (1) A B C D

gained electrons lost electrons gained protons lost protons

(ii) Vicky's hair has also become charged.

Explain how Vicky's hair has become charged.

(2) .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. (iii) Vicky holds the comb over a small piece of metal foil.

The foil jumps up and sticks to the comb.

Show on the diagram where the foil is negatively charged.

(1) (b) Vicky combs her hair with a metal comb.

Then she tries to pick up some small pieces of metal foil with the comb.

The metal comb does not pick up any pieces of metal foil.

Explain why the metal foil is not picked up by the comb.

(2) .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. ..............................................................................................................................................

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(c) The picture shows an electrostatic paint sprayer about to be used to paint a metal object.

When the paint particles leave the sprayer, they are negatively charged.

Explain the benefits of using this sprayer compared with one that does not charge the paint.

(6) .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. ..............................................................................................................................................

(Total for Question is 12 marks)

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Topic 2 – Controlling and using electric currents

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CURRENT AND VOLTAGE Series circuits (first diagram) consist of just one continuous loop – they have no junctions Parallel circuits (second diagram) have different branches, which form separate loops Measuring current: The size of a current (in amps) is measured using an ammeter Ammeters are always placed in ‘series’ with other components in a circuit The electrons aren’t used up and the current leaving the cell is the same as the current that flows back into the cell… o àan ammeter can be placed anywhere in a series circuit…it will always give the same reading (e.g in series circuit below, it’s 0.5 A everywhere)

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Measuring voltage: Potential difference (i.e the voltage) is measured using a voltmeter Voltmeters measure the difference in energy between the electrons going into the component and those coming out – they’re always placed in parallel with the component (i.e on a separate branch): o E.g in the diagram below, the voltmeter is measuring the potential difference (i.e the difference in energy between electrons going in and those coming out) across the light bulb o The higher the potential difference, the more energy emitted from the cellàthe bigger the current…àthe brighter the bulb The potential difference is the energy transferred (to a component) for each unit of charge that passes through that component: o Energy is measured in joules, charge is measured in coulombs o à1 volt = 1 joule per coulomb

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In a parallel circuit, when current reaches a junction, the current splits into two…: o E.g in diagram above, when the 0.5 A current reaches the junction, it splits into 0.2 A and 0.3 A o Note: current is conserved -­‐ i.e none is lost

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CHANGING RESISTANCES Resistance Resistance is a way of measuring how hard it is for electricity to flow – it’s measured in ohms (Ω) The higher the total resistance in a circuit, the smaller the current 18

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àthe current flowing in a circuit can be changed by changing the resistance – this can be done by using a variable resistor (or by putting a different resistor into the circuit) The size of the current flowing in an electric circuit depends on: o the potential difference of the cell/power supply o the resistance of the circuit àrelationship between resistance, current and voltage: o Potential difference (volts, V) = current (amps, A) x resistance (ohms, Ω) o V = I x R o I.e the bigger the voltage and the smaller the resistance, the bigger the current E.g what potential difference is needed to make a 2A current flow through a 10 Ω resistor? o Potential difference = 10 x 2 = 20 V Some electrical components change their resistance depending on the potential difference…

1. Filament lamps: o As the potential difference increases, the filament lamp gets hotter and its resistance increases o àcurrent vs voltage graph flattens off at high voltages 2. Diodes: o Conduct electricity in one direction only o àif a potential difference is applied in the other direction, no current will flow Note… o The resistance of fixed resistors isn’t affected by the potential difference o àin the presence of a fixed resistor there’s a directly proportional relationship (i.e straight line graph) between current and voltage

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Some electrical components change their resistance depending on the conditions surrounding them…

Light-­‐dependent resistor (LDR): o Its resistance is large in the dark and decreases when light is shone on it… i.e the greater the light intensity, the smaller its resistance Thermistors: as the temperature increases, their resistance increases TRANSFERRING ENERGY When current flows through a resistor, energy is transferred to the resistor and it becomes warm This happens with all components…e.g: o in a motor, the main energy transfer is from electrical energy to kinetic (movement) energy o However, some energy is lost/wasted as heat energy Explanation for this transfer of heat energy…: o A current in a wire is a flow of electrons o As the electrons move in a metal, they collide with the ions in the lattice, transferring (heat) energy to them This transfer of heat energy can be beneficial – e.g in electric fires and kettles However, this heating effect of an electric current can cause problems…e.g: o Some electrical appliances can produce so much waste heat energy that they could cause burns if touched o Wires can catch fire if too much current flows – (for this reason, plugs are fitted with fuses which melt and break the circuit if current gets to high) 19

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Calculating power and energy: Power is the energy transferred every second The unit of power is joules per second, or watts (W) – for electrical appliances, the power can be worked out from the current and the potential difference…: o electrical power (watts, W) = current (amps, A) x potential difference (volts, V) o P = I x V E.g a kettle uses the mains electricity supply at 230V. The current is 13 A. What is the power of the kettle? o Power = 13 x 230 = 2990 W The total energy transferred by an appliance depends on its power (i.e voltage x current) and for how long it’s switched on for The energy transferred can be calculated using the equation…: o Energy transferred (joules, J) = current (amps, A) x potential difference (volts, V) x time (seconds, s) o E = I x V x t o I.e the greater the power (voltage x current) and the longer the appliance is switched on for, the more energy is transferred E.g the kettle in the above example takes 2 minutes to boil some water. How much energy does it transfer? o 2 minutes = 120 seconds…… o àenergy transferred by kettle = 13 x 230 x 120 = 358,800J or 358.8 KJ

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Topic 2: Controlling and using electric current

P2 Specification Physics for your future

RAG Current

Topic

P2.2 Specification statements Revised ü 1 2 3

2.1 Be able to describe how an ammeter is placed in series with a component to measure the current, in amps, in the component.

2.2 Be able to explain how current is conserved at a junction.

2.3 Be able to explain how the current in a circuit depends on the potential difference of the source.

2.4 Be able to describe how a voltmeter is placed in parallel with a

component to measure the potential difference (voltage), in volts, across it.

2.5 HT only: Be able to demonstrate an understanding that potential

difference (voltage) is the energy transferred per unit charge passed and hence that the volt is a joule per coulomb.

2.6 Revise any investigations on the relationship between potential

difference (voltage), current and resistance.

2.7 Be able to explain how changing the resistance in a circuit changes the current and how this can be achieved using a variable resistor

2.8 Be able to use the equation:

potential difference (volt, V) = current (ampere, A) x resistance (ohm, Ω) V = I x R 2.9 Be able to demonstrate an understanding of how current varies with potential difference for the following devices

a) filament lamps b) diodes

c) fixed resistors

2.10 Be able to demonstrate an understanding of how the resistance of a light-­‐ dependent resistor (LDR) changes with light intensity

2.11 Be able to demonstrate an understanding of how the resistance of a thermistor changes with change of temperature (negative temperature coefficient thermistors only)

2.12 Be able to explain why, when there is an electric current in a resistor, there is an energy transfer which heats the resistor

2.13 HT only: Be able to explain the energy transfer (in 2.12 above) as

the result of collisions between electrons and the ions in the lattice 2.14 Be able to distinguish between the advantages and disadvantages of the heating effect of an electric current 2.15 Be able to use the equation [appropriate units in ()]:

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P2.2 Exam Questions-­‐ 40 marks, 40 minutes Q7. (a) The diagram shows an electric circuit with two resistors, R and S.

(i) R has a resistance of 11 ohms.

Calculate the potential difference across R. (2)

.............................................................................................................................................. (ii) Use information from the diagram to calculate the current in S. (1) .............................................................................................................................................. (iii) Complete the sentence by putting a cross (

) in the box next to your answer.

A student wants to measure the battery voltage with a voltmeter.

The voltmeter should be placed (1) A B C D

in series with the battery in parallel with the battery in parallel with the ammeter in series with either resistor R or S

(b) Explain why the temperature of a resistor increases when a current passes through it.

(2) .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. ..............................................................................................................................................

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*(c) A resistor is a circuit component.

Two other circuit components are a light dependent resistor (LDR) and a thermistor.

Explain how LDRs and thermistors can be used to control the current in a circuit.

(6)

.............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. ..............................................................................................................................................

(Total for Question is 12 marks)

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Q8. (a) A designer is going to use a thermistor in a temperature gauge. He connects the thermistor into this circuit.

He heats the thermistor and measures the current at different temperatures. Here are some of the results plotted on a graph.

At 47 °C the current was 0.138 A. (i) Plot this value on the graph.

(1) (ii) Draw the curve of best fit through the points.

(1)

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(iii) The supply voltage is 12 V. At 20 °C the current is 0.047 A. Calculate the resistance of the thermistor at this temperature.

(3)

.............................................................................................................................................. (iv) Use this graph of current against temperature to explain the relationship between resistance and temperature for this thermistor.

(2) .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. (b) (i) When there is an electric current in a resistor, the resistor gets hot.

Explain why the resistor gets hot.

(2) .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. (ii) Suggest why the thermistor in a temperature gauge might indicate a temperature slightly higher than the actual temperature of its surroundings.

(1) .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. ..............................................................................................................................................

(Total for Question = 10 marks)

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Q9. (a) Some students investigate the electrical resistance of different components using this circuit.

(i) Which row of the table is correct for both meters P and Q? Put a cross (

) in the box next to your answer.

(1)

A B C D

meter P is an ammeter an ammeter a voltmeter a voltmeter

meter Q is an ammeter a voltmeter a voltmeter an ammeter

(ii) One of the components being investigated is a 12 ohm resistor.

When it is in the circuit, the ammeter reading is 0.50 A. Calculate the voltmeter reading.

(2)

.............................................................................................................................................. (iii) The students reduce the resistance of the variable resistor.

State what happens to the readings on each of the meters P and Q. (2) .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. ..............................................................................................................................................

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(iv) The students then reduce the voltage of the power supply.

State what happens to the current in the circuit.

(1) .............................................................................................................................................. (b) The graphs L, M and N each show how the current in a component varies with the potential difference (voltage) across that component.

Match each graph with the symbol of the component to which it applies.

Draw lines to connect each symbol with its correct graph.

(Total for Question is 8 marks)

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Q10. Using electric current (a) The photograph shows a device used to measure the amount of light.

The circuit diagram shows how the components inside this device are connected.

(i) Complete the sentence by putting a cross ( ) in the box next to your answer.

The meter used in this circuit is (1) A B C D

a voltmeter connected in series with the LDR a voltmeter connected in parallel with the LDR an ammeter connected in series with the LDR an ammeter connected in parallel with the LDR

(ii) The amount of light entering the light-dependent resistor (LDR) increases.

Which row of the table correctly describes the change in the resistance of the LDR and the change in the current in the circuit?

Put a cross ( ) in the box next to your answer.

(1)

A B C D

resistance of the LDR

current in circuit

increases increases decreases decreases

decreases increases decreases increases

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(iii) The device is used as a light meter.

It has a 9 V battery.

Calculate the current when the resistance of the LDR is 600Ω.

(3) current = ........................................ A (iv) When the light meter has been used for a long time, the meter reading becomes incorrect.

Suggest what has happened.

(2) .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. (b) A different light meter has a diode in its circuit.

(i) Explain what happens when the battery is reversed.

(2) .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. (ii) Suggest why the manufacturer of the light meter has included a diode.

(1) .............................................................................................................................................. .............................................................................................................................................. ..............................................................................................................................................

(Total for Question is 10 marks)

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Topic 3 – Motions and forces

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VECTORS AND VELOCITY Displacement: o In a 200m race, all runners cover a 200m distance o However, the track is curvedàthe distance in a straight line between the start and finish is less than this – this distance is called the ‘displacement’ o Displacement is measured in a straight lineàunlike distance (which only has a size), displacement has both a size and direction Speed: o The speed of an object tells you how quickly it will take to travel a certain distance o Speed can be calculated from the equation: § speed (m/s) = distance (m) / time (s) o Like distance, speed only has a size (magnitude) but no direction Velocity: o Velocity tells you how quickly an object is moving, and it also tells you in which direction it’s moving § If object is moving forwards – positive velocity § If object is moving backwards – negative velocity o Velocity, like speed, is measured in m/s Quantities like displacement and velocity – which have a size and direction – are called vector quantities Distance-­‐time graphs: A graph in which distance is plotted against time is called a distance-­‐time graph Time and distance are used to calculate speedàfrom a distance-­‐time graph, we can tell how fast an object is moving: o Horizontal lines mean object is stationary o Straight, sloping lines mean the object is travelling at a constant speed § The steeper the line, the faster the object is travelling o The speed of the object can be calculated from the gradient of the line… § I.e speed = gradient = change in distance / change in time

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E.g graph above…: o Between A and B and between C and D, person is jogging at a steady speed o The person is stationary (not moving) between points B and C o Speed person is jogging at between points C and D: § Point C: 35 minutes, 6km § Point D: 45minutes, 8km § àspeed = gradient = change distance / change in time 30

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§ àspeed = gradient = 2 / 10 = 0.2 km/min = 12 km/hour ACCELERATION Moving things speed up or slow down all the time – this change in velocity is called acceleration Acceleration has both a size and directionàis a vector quantity: o Positive acceleration means the object is speeding up o Negative acceleration means the object is slowing down Acceleration can be calculated from the equation: o acceleration (m/s2) = change in velocity (m/s) / time taken (s) o change in velocity = final velocity (v) -­‐ initial velocity (u) o à a = (v – u) / t E.g racing car starts from 0 m/s and reaches a velocity of 50 m/s in 5 seconds. What is its acceleration? o Acceleration = (50 – 0) / 5 = 10 m/s2 o 10 m/s2 means that each second the velocity of the car increases by 10 m/s (i.e 10 metres per second, per second àunits of acceleration are m/s2) E.g2 during landing, a space shuttle slows down from 70 m/s to 20 m/s in 20s. Calculate its acceleration: o Acceleration = (20 – 70) / 20 = -­‐50/20 = -­‐2.5 m/s2 o The minus sign shows that the space shuttle is slowing down (i.e negative acceleration) VELOCITY-­‐TIME GRAPHS A velocity-­‐time graph shows how the velocity of an object changes with time: o A horizontal line means the object is travelling at a constant velocity § The higher the line, the higher the velocity o A straight sloping line shows the object is accelerating: § The steeper the line, the greater the acceleration § If line slopes upwards, object is speeding up (positive acceleration) § If line slopes downwards, object is slowing down (negative acceleration)

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E.g: o o

At point A -­‐ car is stationary Between points A and B, C and D, E and F, and, G and H – car is accelerating § Between points A and B, C and D and G and H – positive acceleration (car is speeding up) § Between points E and F – negative acceleration (car is slowing down) o Between B and C, D and E, and F and G – car is travelling at a constant velocity o The car is travelling at the highest velocity between points D and E Calculating acceleration from a velocity-­‐time graph: The acceleration of an object between two points can be calculated from a velocity-­‐time graph, using the equation on the previous page E.g acceleration between points C and D (on diagram above): o final velocity = 40 m/s……initial velocity = 20 m/s……time = 1 second o àacceleration = 20 / 1 = 20 m/s2 Calculating distance from a velocity-­‐time graph: The area under a velocity-­‐time graph tells us the distance the object has travelled To calculate the area under a velocity-­‐time graph…

31

o

you split the area under the graph into shapes (squares and triangles), calculate each bit separately, and then add everything together

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E.g (for diagram directly above): o Area of triangle = ½ base x height…à area = 1 x 4 = 4m o Area of square = base x height…àarea = 2 x 4 = 8m o àdistance travelled = 8m + 4m = 12m FORCES Forces can make objects change speed, shape or direction A force is a vector quantity because it has both a size and direction Forces are measured in newtons (N) There are lots of different types of forces: o Upthrust/lift – these act upwards (in air) o Weight (gravity) – this acts downwards o friction/air resistance/drag – these act against the direction of movement (friction – on land, air resistance – in air, drag – in water) o Thrust/driving force – these act in the direction of movement…they are forces produced by engines that push vehicles forwards (thrust – in air, driving force – on land) o Push/pull – these are forces that also act in the direction of movement, but are generated by direct contact between objects (not by engine power) Action and reaction forces: Whenever two objects touch, they interact with each other...: o the forces they exert on each other are equal in size and opposite in direction o These forces are known as ‘action’ and ‘reaction’ forces o As a pair they’re called an ‘action-­‐reaction’ pair E.g a book resting on a table: o The weight of the book exerts a downward force on the table – this is the ‘action force’ o The table exerts an equal and opposite (i.e upward) pushing force on the book -­‐ this is the ‘reaction force’ o Without this reaction force, the book would fall through the table Action and reaction forces are used to propel rockets: o Gases are pushed out from the rear of the rocket – this is the action force o The reaction force from the gases pushes the rocket forwards Free-­‐body force diagrams: A free-­‐body diagram shows the different forces acting on an object:

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The arrows show the direction in which the forces act The length of the arrows shows the size of the forces (the longer the arrow, the bigger the size of the force) RESULTANT FORCES 32

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Resultant force: When more than one force acts on an object, the effect is the same as if they were combined into a single force – the ‘resultant force’ To work out the resultant force, you add together all the forces acting in one direction, and then subtract them from all the forces acting in the opposite direction E.g for the diagram above: o Total thrust force to the left = 100,000 N o Total air resistance force to the right = 25,000 N o àresultant force = 100,000 – 25,000 = 75,000 N of force to the left Balanced forces: Forces that are equal but act in opposite directions are ‘balanced’ When all forces are balanced, the resultant force on an object is zero: o àthe object’s movement, shape or direction will not change o So if object was stationary, it will remain stationary…if it was moving, it will continue to move at the same velocity (i.e it will continue to move at the same speed and in the same direction) Unbalanced forces: If forces acting in opposite directions are not equal, the forces are ‘unbalanced’ When forces are unbalanced, the resultant force on an object is not zeroàthe object will accelerate in the direction of the resultant force In the diagram above…: o The thrust is the force produced by the plane’s engines, moving the plane forwards o As the plane flies, air molecules push against the plane, producing an opposite force called air resistance o The thrust is greater than the air resistance (as thrust arrow is longer): § àforces are unbalancedàthere’s a resultant force in the direction of the thrust force § àplane accelerates in the direction of the thrust force (left) (i.e plane’s velocity increases) If thrust and air resistance forces were balanced, then the resultant force would be zero and the plane would continue to fly at the same velocity If air resistance was greater than the thrust force…: o there would be a resultant force in the direction of air resistance o àthere would be a (negative) acceleration in the direction of the air resistance (right) (i.e the plane’s velocity would decrease) Note: remember when answering questions on forces that there are no air particles in space (space is a vacuum)àthere is no air resistance in space FORCES AND ACCELERATION The rate at which an object accelerates depends on…: o the size of the (resultant) force – the greater the resultant force, the greater the acceleration of the object o the mass of the object – the greater the mass of the object, the smaller its acceleration àequation linking acceleration, force and mass: o Force (N) = mass (kg) x acceleration (m/s2) o F = m x a o 1 newton is the force needed to accelerate a mass of 1kg by 1m/s2 E.g a car’s acceleration is 3 m/s2. It weighs 1500kg. What is the force provided by the engine? o Force = 1500 x 3 = 4,500 N TERMINAL VELOCITY Mass and weight: Mass (measured in kg) is the quantity of matter there is in an object and does not change Weight (measured in N) is a measure of the pull of gravity on an object…àif gravity changes, weight also changes The strength of gravity is called the ‘gravitational field strength’ (measured in N/kg) On earth, the gravitational field strength is 10N/kgàeach kilogram is pulled down with a force of 10N The weight of any object on earth can be calculated using the equation: o weight (N) = mass (kg) x gravitational field strength (N/kg) 33

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o W = m x g E.g what is the weight of a 75kg person on Earth? o weight = 75 x 10 = 750 N E.g2 what is the weight of a 75kg person on the moon? The moon’s gravitational field strength is about 1.5N/kg… o Weight = 75 x 1.5 = 112.5 N o Notice how person’s mass (75kg) is the same on the moon as it is on Earth -­‐ mass never changes (it’s not affected by gravitational field strength) o Person’s weight instead is much lower on the moon (112.5 N) than on Earth (750 N) because the gravitational field strength is much smaller on the moon than on the Earth Acceleration of falling objects: Larger masses need more force to get them to accelerate than smaller masses (recall the equation: force = mass x acceleration) But as the mass increases, so does the force from gravity (weight) (recall the equation: weight = mass x gravitational field strength) On Earth, there are air particles, which generate air resistance: o àif a hammer and a feather are dropped, the hammer hits the ground first because it is slowed down less by air resistance However, in space there are no air particles and so no air resistance…: o àin a vacuum, all objects (regardless of their mass) accelerate down towards the Earth by the same amount o àif a hammer and a feather are dropped in space, they hit the ground at the same time Terminal velocity – skydiver example: When a skydiver first starts to fall, the main force acting on the skydiver is his own weight (acting downwards)…there is very little air resistance acting in the opposite direction (i.e upwards)… o àlarge resultant force downwards o àskydiver accelerates quickly towards the ground As the skydiver gains velocity, the size of the air resistance force increases… o àthe resultant force downwards is smaller o àskydiver is still accelerating down towards the ground, but the size of the acceleration is smaller Eventually the weight and air resistance become balanced… o àresultant force is now zero o àskydiver stops accelerating…i.e the skydiver continues to fall towards the ground, but now at a constant velocity This constant (maximum) velocity reached when the air resistance force balances the weight is called the ‘terminal velocity’

34

Topic 3: Motion and Forces

P2 Specification Physics for your future

RAG Current

Topic

P2.3 Specification statements Revised ü 1 2

3

3.1 Be able to demonstrate an understanding of the following as vector quantities: a) displacement b) velocity c) acceleration d) force 3.2 Be able to interpret distance/time graphs including determination of speed from the gradient.

3.3 Know that velocity is speed in a stated direction 3.4 Be able to use the equation: speed (m/s) = distance (m) / time (s) s = d / t 3.5 Be able to use the equation: acceleration (metre per second squared, m/s2) = change in velocity (metre per second, m/s) / time taken (second, s) a = (v -­‐ u) / t 3.6 Be able to interpret velocity/time graphs to: a) compare acceleration from gradients qualitatively b) calculate the acceleration from the gradient (for uniform acceleration only) c) determine the distance travelled using the area between the graph line and the time axis (for uniform acceleration only 3.7 Be able to draw and interpret a free-­‐body force diagram

3.8 Be able to demonstrate an understanding that when two bodies interact, the forces they exert on each other are equal in size and opposite in direction and that these are known as action and reaction forces 3.9 Be able to calculate a resultant force using a range of forces (limited to the resultant of forces acting along a line) including resistive forces

3.10 Be able to demonstrate an understanding that if the

resultant force acting on a body is zero, it will remain at rest or continue to move at the same velocity

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3.11 Be able to demonstrate an understanding that if the resultant force acting on a body is not zero, it will accelerate in the direction of the resultant force 3.12 Be able to demonstrate an understanding that a resultant force acting on an object produces an acceleration which depends on: a) the size of the resultant force b) the mass of the object 3.13 Be able to use the equation: force (newton, N) = mass (kilogram, kg) x acceleration (metre per second squared, m/s2) F = m x a 3.14 Be able to use the equation: weight (newton, N) = mass (kilogram, kg) x gravitational field strength (newton per kilogram, N/kg) W = m x g 3.15 Revise any investigations on the relationship between force, mass and acceleration

3.16 Know that in a vacuum all falling bodies accelerate at the same rate

3.17 Be able to demonstrate an understanding that:

a) when an object falls through an atmosphere air resistance increases with increasing speed

b) air resistance increases until it is equal in size to the weight of the falling object

c) when the two forces are balanced, acceleration is zero and terminal velocity is reached

36

P2.3 Exam Questions-­‐ 41 marks, 41 minutes.

Q11. (a) A car is travelling along a level road.

(i) Complete the sentence by putting a cross (

) in the box next to your answer.

When the velocity of the car is constant, the force of friction on it is (1) A B C D

zero greater than the driving force smaller than the driving force the same size as the driving force

(ii) The car now accelerates in a straight line.

Its average acceleration is 12 m/s2.

Calculate the increase in velocity of the car in 4.0 s.

(3)

.............................................................................................................................................. (b) This table shows data about two other cars.

The owner of the family car claims that although the sports car has greater acceleration, it produces a smaller accelerating force than his family car.

Explain how these figures support his claim.

(2) .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. ..............................................................................................................................................

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*(c) After going to the shops, a car driver places a bag of shopping on the passenger seat.

During the journey home, the driver has to use the brakes to stop very suddenly. The driver is wearing a seat belt.

Explain what happens next to the car, the driver and the shopping bag.

(6)

.............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. ..............................................................................................................................................

(Total for Question = 12 marks)

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Q12.

A water tank drips water.

(a) Scientists could use four quantities to describe the movement of the water drops.

Three of these quantities are vectors.

The other quantity is a scalar. acceleration

force

(i) Complete the sentence by putting a cross (

mass

velocity

) in the box next to your answer.

The scalar quantity is (1) A B C D

acceleration force mass velocity

(ii) Complete the following sentence using one of the quantities from the word box above.

(1) In a vacuum, all bodies falling towards the Earth's surface have the same . . . . . . . . . . . . . . . . . . ..... (b) The mass of one water drop is 0.000 08 kg.

Calculate its weight. (gravitational field strength is 10 N/kg) (2)

weight = . . . . . . . . . . . . . . . . . . . . . . N (c) The water drop falls to the ground, 13 m below, in 1.7 s.

Calculate the average speed of the drop while it is falling.

(2)

average speed = . . . . . . . . . . . . . . . . . . . . . . m/s 39 Â

*(d) The tank is a long way above the ground.

It drips at a steady rate.

The first drawing shows water drops which have just left the tank.

The second drawing shows water drops which are near to the ground.

Explain why the drops which are near to the ground are an equal distance apart but the drops which have just started to fall are not.

(6) .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. ..............................................................................................................................................

(Total for Question is 12 marks) 40 Â

Q13.

Forces and motion The graph shows a velocity-time graph for a cyclist over a time of 60 s.

(a) (i) When is the cyclist travelling with greatest velocity?

Put a cross ( ) in the box next to your answer.

(1) A B C D

for the first 15 seconds between 15 and 40 seconds between 40 and 50 seconds for the last 10 seconds

(ii) Calculate how long the cyclist is stationary for.

(1) answer = .................................... seconds (b) The cyclist in this picture is travelling at a constant velocity.

Her muscles produce a driving force of 15 N.

Draw an arrow on the diagram to show the size and direction of the overall resistive force acting on the cyclist.

(1)

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(c) The cyclist accelerates at 1.4 m/s2.

The mass of the cyclist and bicycle is 60 kg. (i) Calculate the resultant force.

(2) resultant force = ....................................... N (ii) The cyclist accelerates for 8 s.

Calculate the increase in velocity during this time.

(3) increase in velocity = ............................... m/s

(Total for Question is 8 marks)

42 Â

Q14.

The graph shows how the velocity of a small car changes with time.

(a) Complete the sentence by putting a cross (

) in the box next to your answer.

The resultant force on the car will be zero when the car is (1) A B C D

accelerating decelerating changing velocity moving at a constant velocity

(b) (i) Use the graph to estimate the velocity of the car at three seconds.

(1) .............................................................................................................................................. (ii) Calculate the acceleration of the car when it is speeding up.

(2)

acceleration = . . . . . . . . . . . . . . . . . . . . . . m/s2 (iii) Explain why the units of acceleration are m/s2.

(2) .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. (iv) Show that the car travels further at a constant velocity than it does when it is slowing down.

(3) .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. ..............................................................................................................................................

(Total for Question is 9 marks) 43 Â

Topic 4 – Momentum, energy, work and power • • • • • • • •

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STOPPING DISTANCES Stopping safely: When a driver sees a problem ahead, the car travels some distance before the driver reacts and steps on the brakes – this is called the ‘thinking distance’ Once the driver has stepped on the brakes, the car will travel some distance before it comes to a complete stop – this is called the ‘braking distance’ The overall ‘stopping distance’ for a car = thinking distance + braking distance Factors affecting stopping distances: Note: make sure you realise that some factors affect just the thinking distance, some just the braking distance, and some affect both 1. Person’s reaction time (i.e time it takes to respond to danger): o The slower a person’s reaction time, the longer the thinking distance o Tiredness, illness, or taking drugs or alcohol can all slow down reaction times 2. Speed of the vehicle: o The faster the vehicle is travelling, the longer both the thinking distance and the braking distance 3. State of the car’s brakes and road conditions: o For a car to come to a stop there must be friction created between the car’s tyres and the road… § the more friction between the tyres and the road, the smaller the braking distance o The amount of friction between the tyres and the road depends on: § the condition of the car’s brakes (the better the brakes, the more friction they createàshorter braking distance) § condition of the road surface (e.g if the road is wet or has loose gravel, less friction is createdàlonger braking distance) o Note: due to longer braking distances in wet conditions, drivers should leave more of a gap between their car and the car in front when it is raining 4. Mass of the vehicle: o If a vehicle has more mass, more force is needed to make it slow down o àthe heavier the vehicle, the longer the braking distance MOMENTUM Momentum is a measure of how strongly something is moving… o momentum (kg m/s) = mass (kg) x velocity (m/s) o I.e the heavier the vehicle and the faster it is travelling, the greater its momentum E.g what is the momentum of a monster truck (mass = 4500kg) when travelling at 12m/s, in an eastward direction? o Momentum = 45000 x 12 = 54,000 kg m/s east Momentum has a size and direction so is a vector quantity: o àwhen giving an answer, you should state not only the amount of momentum an object has (the ‘size’) but also the direction of that momentum (which will be in the same direction as the velocity) Conservation of momentum: When a moving object collides with another object: o their masses are added togetheràtheir combined speed will be slower o However, the total momentum of both objects is the same before the collision as it is after the collision -­‐ this is known as ‘conservation of linear momentum’ E.g:

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Before collision: o Object on the left has a momentum = 15 x 4 = 60 kg m/s to the right o Object on the right has a momentum = 0 x 2 = 0 kg m/s After collision: o Combined objects have a momentum = 10 x 6 = 60 kg m/s to the right àthe combined momentum of the objects before and after the collision is the same This demonstrates that when objects collide, momentum is conserved (i.e it is transferred to the other object without any being lost) MOMENTUM AND SAFETY When travelling in a car, passengers are going at the same speed as the car If a car brakes suddenly, there’s a rapid change in momentum, and a strong force is applied to the passengers -­‐ this can result in serious injury (e.g passengers can smash their heads against the windscreen) The ‘rate of change of momentum’ (i.e the speed at which the momentum of an object changes) is equal to the force applied to the object…: o The rate of change of momentum = change in momentum / time taken for that change o àforce (N) = change in momentum (kg m/s) / time taken for that change (s) o E.g what is the force needed to change a cyclist’s momentum by 24 kg m/s in 4 seconds? § Force = 24 / 4 = 6 N So in a car crash…: o the quicker the rate of change of momentum (i.e the quicker the passenger’s momentum decreases to 0), the more force applied to the passengersàthe more likely the passengers are to get hurt o àsafety measures in cars try to reduce the rate of change of momentum of passengers (i.e they try to increase the time it takes for the passenger’s momentum to decrease to 0) so that force applied to the passengers is smaller Note: the ‘rate of change of momentum’ is basically the same as saying the ‘rate of change of velocity’ because the time it takes for velocity to decrease to 0 is the same time it takes for momentum to decrease to 0 (momentum = velocity x mass) o Indeed, equation above can be re-­‐written as…: § force = [(final velocity x mass) – (initial velocity x mass)] / time § F = (mv – mu) / t Vehicle safety measures: 1. Seat belts: o In an accident, seat belts stretchàpassenger’s velocity is slowed down more gradually o àit takes longer for passenger’s momentum to be slowed to zero (i.e the rate of change of momentum is reduced) o àforce applied to the passengers is less o àreduced chance of injury However, in high speed accidents, the force is so great that the seat belt by itself could still cause injury…à 2. cars are also fitted with airbags -­‐ these work in the same way as seat belts, reducing the rate of change of momentum 3. Cars also have crumple zones: o In an accident, the material in these crumple zones squashes and folds in a specific way o This crumpling and folding reduces the momentum of the car over a longer period of time (i.e reduces the rate of change of momentum) o àthe impact forces on the passengers are less o àreduced chance of serious injury WORK AND POWER ‘Work’ is done when energy is transferred from one form to another o E.g car brakes ‘do work’ by transferring kinetic energy to thermal energy The amount of ‘work’ done is equal to the amount of energy transferred Energy is measured in joules (J)àwork is also measured in joules Calculating work done: work done (joules, J) = force (newtons, N) x distance moved in the direction of the force (metres, m) o E = F x d E.g a sailor lifts a 300 N sail from the deck to a height 4 m up. How much work does the sailor do? o Work done = 300 x 4 = 1,200 J 45

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Power: Power is the rate of doing work – measured in watts (W) Power (watt, W) = work done (joule, J) / time taken (second, s) o P = E / t o 1 watt = 1 joule of work done per second o I.e the more work done per second, the more power generated E.g a motorbike engine increases the bike’s kinetic energy over 40m, using a force of 6000 N. It takes 5 seconds to do this. What power did the engine provide? o Work done = 6000 x 40 = 240,000 J o àpower = 240,000 / 5 = 48,000 W POTENTIAL AND KINETIC ENERGY Gravitational potential energy: Gravitational potential energy is energy that is stored because of an object’s position in a gravitational field o I.e: on Earth, if something can fall (e.g a person on a diving board) it has gravitational potential energy Gravitational potential energy can be calculated using the equation…: o Gravitational potential energy (J) = mass (kg) x gravitational field strength (N/kg) x vertical height from ground (m) o GPE = m x g x h E.g on earth the strength of the gravitational field is 10N/kg. What is the gravitational potential energy gained by a 500kg Mars Rover when it’s lifted 15m by a test crane on Earth? o GPE = 500 x 10 x 15 = 75,000 J Kinetic energy: Kinetic energy is another name for movement energy The kinetic energy can be calculated using the equation…: o kinetic energy (J) = ½ x mass (kg) x (velocity)2 (m/s2) o KE = ½ x m x v2 E.g what is the kinetic energy of a 65kg girl running at 6m/s? o KE = ½ x 65 x (62) = 1,170 J Conservation of energy: When energy is transferred from one form to another, energy is conserved (i.e total amount always remains the same…none is lost) E.g: o As an object falls, its gravitational potential energy is converted into kinetic energy o When an object with gravitational potential energy falls down, the amount of kinetic energy it has just before it hits the ground is equal to its initial gravitational potential energy (as all the GPE has been converted to KE) E.g when a 500kg item was dropped, 75000 J of gravitational potential energy were all transferred to kinetic energy by the time it hit the ground. How fast did the item land? o KE = 75000 J (because as item falls all 75000 J of GPE is transferred to KE) o à(velocity)2 = 75000 / (½ x 500) = 300 o àvelocity = √300 = 17.3 m/s Braking distances, conservation of energy, and work done: Brakes ‘do work’ by transferring kinetic energy to thermal energy When the vehicle stops, it has no more kinetic energy (energy is conservedàall the kinetic energy has been converted to thermal energy) àthe work done to bring a vehicle to rest is equal to its initial kinetic energy… o i.e the greater the initial velocity of the vehicle, the greater its initial kinetic energy (recall: KE = ½ x m x v2)àthe more work that needs to be done to bring the vehicle to rest o This explains why the faster a vehicle is travelling, the longer its braking distance

46

Topic 4: Momentum, energy, work and power

P2 Specification Physics for your future

RAG Current

Topic

P2.4 Specification statements Revised ü 1 2

3

4.1 Know that the stopping distance of a vehicle is made up of the sum of the thinking distance and the braking distance

4.2 Be able to demonstrate an understanding of the factors affecting the stopping distance of a vehicle, including: a) the mass of the vehicle b) the speed of the vehicle

c) the driver’s reaction time

d) the state of the vehicle’s brakes

e) the state of the road

f) the amount of friction between the tyre and the road surface 4.3 Revise any investigations on the forces required to slide blocks along different surfaces, with differing amounts of friction 4.4 Be able to use the equation: momentum (kilogram metre per second, kg m/s) = mass (kilogram, kg) x velocity (metre per second, m/s) to calculate the momentum of a moving object momentum = mass x velocity momentum = mv 4.5 Be able to demonstrate an understanding of momentum as a vector quantity 4.6 Be able to demonstrate an understanding of the idea of linear momentum conservation 4.7 Be able to demonstrate an understanding of the idea of rate of change of momentum to explain protective features including bubble wraps, seat belts, crumple zones and air bags 4.8 Revise any investigations on how crumple zones can be used to reduce the forces in collisions 4.9 HT only: Be able to use the equation: force (newton, N) = change in momentum (kilogram metre per second, kg m/s) / time (second, s) F = (mv -­‐ mu) / t to calculate the change in momentum of a system, as in 4.6 4.10 Be able to use the equation: work done (joule, J) = force (newton, N) x distance moved in

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the direction of the force (metre, m) E = F x d 4.11 Be able to demonstrate an understanding that energy transferred (joule, J) is equal to work done (joule, J) 4.12 Know that power is the rate of doing work and is measured in watts, W 4.13 Be able to use the equation: power (watt, W) = work done (joule, J) / time taken (second, s) P = E / t 4.14 Know that one watt is equal to one joule per second, J/s 4.15 Be able to use the equation: gravitational potential energy (joule, J) = mass (kilogram, kg) x gravitational field strength (newton per kilogram, N/kg) x vertical height (metre, m) GPE = m x g x h 4.16 Be able to use the equation: kinetic energy (joule, J) = 1/2 mass (kilogram, kg) x velocity2 ((metre/second)2, (m/s)2) KE = 1/2mv2 4.17 Be able to demonstrate an understanding of the idea of conservation of energy in various energy transfers 4.18 HT only: Be able to carry out calculations on work done to show the dependence of braking distance for a vehicle on initial velocity squared (work done to bring a vehicle to rest equals its initial kinetic energy).

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P2.4 Exam questions – 41 marks, 41 minutes.

Q15.

A 60 kg student weighs 600 N. He does a bungee jump.

The bungee cord becomes straight and starts to stretch when he has fallen 50 m. (a) Complete the sentence by putting a cross ( He first stops moving

) in the box next to your answer.

(1)

A B C D

before all the energy has disappeared before the bungee cord starts to stretch when the bungee cord is stretched the most when the elastic potential energy is zero

(b) Complete the sentence by putting a cross (

) in the box next to your answer.

When his speed is 10 m/s his momentum is (1) A B C D

600 kg m/s 3 000 kg m/s 6 000 N m/s 30 000 N m/s

(c) (i) Calculate the change in gravitational potential energy as the student falls 50 m.

Give the unit.

(3)

.............................................................................................................................................. (ii) State at what point in the bungee jump the student has maximum kinetic energy.

(1) .............................................................................................................................................. ..............................................................................................................................................

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(iii) Explain why his maximum kinetic energy is likely to be less than your answer to (c)(i).

(2) .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. ..............................................................................................................................................

(Total for Question = 8 marks) Q16.

Andrew skis down a hill.

(a) Andrew starts from the top of the hill and his speed increases as he goes downhill.

He controls his speed and direction by using his skis.

He brings himself to a stop at the bottom of the hill.

Describe the energy changes that happen between starting and stopping.

(3) .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. (b) Andrew returns to the top of the hill and starts again. (i) His mass is 67 kg.

Show that his momentum is about 2000 kg m/s when his velocity is 31 m/s.

(2)

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(ii) He falls over when his momentum is 2000 kg m/s.

After he falls over, he slows down by sliding across the snow.

It takes 2.3 s for his momentum to reduce to zero.

Calculate the average force on Andrew as he slows down.

(2)

.............................................................................................................................................. (iii) Andrew is not injured by the fall even though he was moving quickly.

Use ideas about force and momentum to explain why he is not injured.

(2) .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. ..............................................................................................................................................

(Total for Question is 9 marks)

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Q17. Momentum, energy and forces A box with a mass of 0.8 kg is lifted from the floor and placed on a shelf.

The shelf is 1.8 m above the floor.

(a) (i) The box has gained gravitational potential energy.

Calculate the gain in gravitational potential energy.

Gravitational field strength = 10 N/kg (2)

gain in gravitational potential energy = ......................................... J (ii) The box falls off the shelf.

State the kinetic energy of the box just before it hits the floor.

(1) ....................................................................... J (iii) Just before the box hits the floor it has a momentum of 4.8 kg m/s.

Calculate the velocity of the box just before it hits the floor.

(3)

velocity = ........................................ m/s

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*(b) The items in the box are packed in bubble wrap to protect them from damage.

Explain, by considering changes either in momentum or in kinetic energy, how bubble wrap protects the items in a box from damage caused by a fall.

(6) .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. ..............................................................................................................................................

(Total for Question is 12 marks)

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Q18.

A child is stationary on a swing.

(a) The child is given a push by his brother to start him swinging.

His brother applies a steady force of 84 N over a distance of 0.25 m. (i) Calculate the work done by this force.

(2) .............................................................................................................................................. (ii) State how much energy is transferred by this force.

(1) .............................................................................................................................................. (iii) After several more pushes, the child has a kinetic energy of 71 J. The mass of the child is 27 kg.

Show that the velocity of the child at this point is about 2.3 m/s.

(2) (iv) Which one of these quantities changes in both size and direction while he is swinging?

Put a cross (

) in the box next to your answer.

(1)

A B C D

his gravitational potential energy his momentum the force of gravity acting on him his kinetic energy

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*(b) The brother then stops pushing the child.

The graph shows how the kinetic energy of the child varies over the next few swings.

Explain the energy changes during this time.

(6) .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. ..............................................................................................................................................

(Total for Question is 12 marks)

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Topic 5 – Nuclear fission and nuclear fusion

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Atoms contain protons, neutrons and electrons – these are sub-­‐atomic particles Protons and neutrons are in the nucleus…electrons surround the nucleus o Protons have a charge of +1, neutrons have no charge, electrons have a charge of -­‐1 o In an atom, the number of electrons = number of protonsàatoms have no overall charge Atomic number – number of protons in the nucleus of an atom… o All atoms of a particular element have the same number of protonsàsame atomic number o Atoms of different elements have different numbers of protons (àno two elements have the same atomic number) Mass number – total number of protons and neutrons in the nucleus of an atom… o The number of neutrons in an atom can vary In a chemical symbol, e.g , the atomic number is the bottom number (the smaller one) and the mass number is the top number (the bigger one) Isotopes: Isotopes are different atoms of an element with the same number of protons, but different numbers of neutrons (i.e same atomic number, different mass number) E.g atoms of lithium can exist as lithium-­‐6 and lithium-­‐7: o The number attached is the mass number of the isotope… § The nucleus of an atom of lithium-­‐6 has 3 protons and 3 neutrons àits mass number = 6 § The nucleus of an atom of lithium-­‐7 has 3 protons and 4 neutrons àits mass number = 7 IONISING RADIATION Radioactive substances have unstable nuclei that emit ionising radiation (this is a random process As they emit ionising radiation, unstable nuclei lose (release) energy and decay to become more stable Ionising radiation is radiation that has enough energy to cause atoms to lose electrons and become (positively charged) ions There are three main types of ionising radiation -­‐ alpha particles, beta particles and gamma rays Properties of ionising radiations: Alpha particles: o contain two protons and two neutrons (same as the nucleus of a helium atom) o have no electrons o àthey have a charge of +2 Beta particles: are electronsàare negatively charged Gamma rays: o are high-­‐frequency electromagnetic wavesàtravel at the speed of light o they have no charge Ability of ionising radiations to ionise atoms and penetrate materials: Alpha particles: o Very ionising (i.e they easily make atoms lose electrons and become ions) o Each time ionising particles ionise an atom, they lose some energy o àalpha particles lose energy quickly so don’t travel far into matter -­‐ i.e they have a ‘short penetration distance’ § So alpha particles can be stopped by a few centimetres of air or a few millimetres of paper Beta particles: o Moderately ionising (less than alpha particles, more than gamma rays) o àlose energy less quickly than alpha particlesàthey can penetrate further into matter than alpha particles can § Beta particles can be stopped by a few millimetres of aluminium Gamma rays: o Weakly ionising (much less than both alpha and beta particles) o àlose energy very slowlyàcan penetrate further into matter than both alpha and beta particles can § àGamma rays need thick lead to stop them 56

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NUCLEAR REACTIONS Radioactive decay: The process of radioactive decay releases energy… o when alpha and beta particles are emitted from unstable nuclei at high speeds, kinetic energy is released o when gamma rays are emitted from unstable nuclei at the speed of light, the energy released is in the form of electromagnetic radiation Other nuclear reactions also release energy…

Nuclear fission: Some large unstable nuclei can split into two smaller nuclei called daughter nuclei – this process is called nuclear fission: o E.g when a uranium-­‐235 absorbs a neutron it becomes unstable and immediately splits it into two smaller daughter nuclei, and two or more neutrons are released

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Nuclear fission releases a huge amount of energy…: o Most is in the form of kinetic energy because both daughter nuclei and neutrons are moving at high speeds o Some thermal energy is also released Nuclear fission -­‐ uncontrolled chain reactions: When a uranium-­‐235 nucleus splits, the neutrons released can be absorbed by other uranium-­‐235 nuclei…: o These other uranium-­‐235 nuclei will split into two smaller daughter nuclei and release more neutrons o These neutrons can then be absorbed by yet more uranium-­‐235 nuclei …and so on… o This is called an ‘uncontrolled chain reaction’… § In uncontrolled chain reactions, lots of energy is released (through nuclear fission) in a very short time – this occurs in an atomic bomb Nuclear fission -­‐ controlled chain reactions: If some of the neutrons released during nuclear fission are absorbed by other materials, then chain reactions can be controlled…

E.g: o when a uranium-­‐235 nucleus splits, all neutrons except for one are absorbed by other materials o àonly one neutron from each fission event can be absorbed by another uranium-­‐235 nucleus o The chain reaction is now ‘controlled’ because the chain reaction continues at a constant rateàthe amount of energy produced through nuclear fission is regulated Controlled chain reactions occur in nuclear reactors (see below)

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NUCLEAR FISSION IN NUCLEAR REACTORS Nuclear reactors in nuclear power stations convert (nuclear) energy contained in the nuclei of uranium and plutonium ions into thermal energy using nuclear fission The rate at which nuclear energy is transferred to thermal energy is kept constant by controlling the fission chain reaction… o This is done by ensuring that only one of the neutrons released by the decay of a uranium nucleus is absorbed by another uranium nucleus o To achieve this, the extra neutrons that are released have to be absorbed – this is done by control rods in the reactor core…

Control rods: Control rods contain elements that absorb neutrons… o If the rate of fission needs to be increased, the control rods are moved out of the coreàfewer neutrons are absorbed by control rodsàmore neutrons can be absorbed by other uranium nuclei o If the rate of fission needs to be decreased, more control rods are moved into the coreàmore neutrons are absorbed by control rodsàfewer neutrons can be absorbed by other uranium nuclei When the control rods are fully lowered into the reactor core, they absorb all the neutronsàthe chain reaction stops and the reactor shuts down Moderators: Neutrons emitted from the fission of a uranium-­‐235 nucleus are moving very fast To make them more likely to be absorbed by other uranium-­‐235 nuclei, they need to be slowed down – this is done by moderators in the reactor core Generating electricity: 1. Thermal energy from the core is transferred to the coolant (usually water at high pressure), which is pumped through the reactor 2. This super-­‐heated water is pumped to a ‘heat exchanger’ where it’s used to produce steam 3. The steam drives a turbine, which turns a generator 4. The generator transfers kinetic energy into electrical energy Radioactive waste: The products of nuclear fission (i.e the daughter nuclei and radioactive isotopes) are radioactive àover time, radioactive waste builds up in the reactor core NUCLEAR FUSION Nuclear fusion occurs when small nuclei combine to form larger nuclei E.g when hydrogen nuclei fuse to form helium…: o There are two isotopes of hydrogen: § Hydrogen-­‐2 called deuterium (1 proton, 1 neutron) § Hydrogen-­‐3 called tritium (1 proton, 2 neutrons) o When tritium and deuterium nuclei fuse, helium is formed…: § Helium has 2 protons and 2 neutrons § àone neutron is freed from the nucleus, releasing a huge amount of energy So much energy is released in nuclear fusion reactions that they are the energy source for stars, including our Sun Nuclear fusion is being investigated by scientists as a possible energy source for the future… o Unlike nuclear fission, nuclear fusion doesn’t produce any radioactive waste productsàwould be a better alternative Conditions for fusion: The nuclei of both deuterium and tritium are positively charged (due to presence of 1 proton in each nucleus)àthey repel – this is called ‘electrostatic repulsion’ So in order for deuterium and tritium nuclei to collide and fuse (i.e to overcome the electrostatic repulsion between protons), the conditions must be right…

1. High pressure: o For nuclei to fuse, they need to get very close to each other o The Sun has a very strong gravitational field, which creates high densities (i.e lots) of nuclei at its centre… § if the density of nuclei is high, then collisions are much more likely to happen o These conditions are not present on Earth, but very high pressures (which increase the density of nuclei) can be produced inside fusion reactors 58

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2. High temperature: o If nuclei are travelling fast enough, some can overcome their electrostatic repulsion and collide o The higher the temperature, the faster the nuclei moveàthe more likely they are to overcome their electrostatic repulsion and collide Unfortunately, the conditions that are required for nuclear fusion (very high temperature and pressure) are difficult to achieve and are very expensive àit will be some time before fusion energy will become a viable energy source *Note* -­‐ Cold fusion: Scientists 20 years ago claimed to have carried out nuclear fusion at 50°C – this became known as ‘cold fusion’ The possibility of carrying out nuclear fusion at low temperatures was exciting at the time because it would be more convenient and less expensive However, attempts to repeat the original findings have failed (i.e the cold fusion theory has not been ‘validated’)àmost scientists do not believe cold fusion can happen

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Topic 5: Nuclear Fission and nuclear fusion

P2 Specification Physics for your future

RAG Current

Topic

P2.5 Specification statements Revised ü 1 2 3

5.1 Be able to describe the structure of nuclei of isotopes using the terms atomic (proton) number and mass (nucleon) number and using symbols in the format 146C

5.2 Be able to explain how atoms may gain or lose electrons to form ions.

5.3 Know that alpha and beta particles and gamma rays are ionising radiations emitted from unstable nuclei in a random process.

5.4 Know that an alpha particle is equivalent to a helium nucleus, a beta particle is an electron emitted from the nucleus and a gamma ray is electromagnetic radiation 5.5 Be able to compare alpha, beta and gamma radiations in terms of their abilities to penetrate and ionise.

5.6 Be able to demonstrate an understanding that nuclear reactions can be a source of energy, including fission, fusion and radioactive decay.

5.7 Be able to explain how the fission of U-­‐235 produces two daughter nuclei and two or more neutrons, accompanied by a release of energy.

5.8 Be able to explain the principle of a controlled nuclear chain reaction.

5.9 Be able to explain how the chain reaction is controlled in a nuclear reactor including the action of moderators and control rods.

5.10 Be able to describe how thermal (heat) energy from the chain reaction is converted into electrical energy in a nuclear power station.

5.11 Know that the products of nuclear fission are radioactive.

5.12 Be able to describe nuclear fusion as the creation of larger nuclei from smaller nuclei, accompanied by a release of energy and recognise fusion as the energy source for stars.

5.13 Be able to explain the difference between nuclear fusion and nuclear fission.

5.14 HT only: Be able to explain why nuclear fusion does not happen at low temperatures and pressures, due to electrostatic repulsion of protons.

5.15 HT only: Be able to relate the conditions for fusion to the difficulty of making a practical and economic form of power station.

5.16 Be able to demonstrate an understanding that new scientific theories, such as ‘cold fusion’, are not accepted until they have been validated by the scientific community.

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P2.5 Exam Questions – 43 marks, 43 minutes.

Q19.

Alpha, beta and gamma are types of ionising radiation. (a) State two ways in which gamma radiation is different from alpha radiation.

(2) .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. (b) (i) Complete the sentence by putting a cross (

) in the box next to your answer.

A beta particle is emitted by (1) A B C D

an alpha particle a fusion particle a gamma ray an unstable nucleus

(ii) Complete the sentence by putting a cross (

) in the box next to your answer.

A beta particle has an identical charge to (1) A B C D

an alpha particle an electron a neutron a nucleus

(c) Explain how an atom becomes ionised by radiation.

(2) .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. ..............................................................................................................................................

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*(d) The removable lens of this old camera has four pieces of glass in it.

One of the pieces of glass is radioactive. Its surface is covered with a thin layer of magnesium fluoride.

Radioactive isotopes in the glass emit alpha, beta and gamma radiation in all directions.

A scientist removes the lens from the camera. She measures the radiation coming from the back, front and side of the lens.

The amount of radiation is different in each direction.

No alpha radiation is detected.

The readings are shown on the diagram.

Explain why the readings in the three directions are different.

(6) .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. ..............................................................................................................................................

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(Total for Question is 12 marks)

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Q20. (a) Two isotopes of uranium are U-235 and U-238.

Here are the symbols of the nuclei of these isotopes.

(i) Complete the sentence by putting a cross (

) in the box next to your answer.

The U-235 isotope has (1) A B C D

the same number of neutrons as U-238 the same number of protons as U-238 more neutrons than U-238 more protons than U-238

(ii) U-235 is radioactive.

When it decays, it releases an alpha particle.

Describe an alpha particle.

(2) .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. (b) U-235 can also be made to undergo fission.

Describe what happens during nuclear fission.

(4) .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. ..............................................................................................................................................

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(c) Fission is used in nuclear reactors.

Graphite is used as a moderator in nuclear reactors.

Explain why a moderator is needed in a nuclear reactor.

(2) .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. ..............................................................................................................................................

(Total for Question is 9 marks) Q21. Nuclear reactions (a) Complete the sentence by putting a cross ( ) in the box next to your answer.

Two types of nuclear reaction are nuclear fission and nuclear fusion.

Nuclear fission and nuclear fusion reactions both (1) A B C D

combine hydrogen nuclei combine uranium nuclei release neutrons release energy

(b) In 1989, two scientists called Pons and Fleischmann claimed to have produced ‘cold fusion’.

Their claim has never been validated by the scientific community.

Explain the phrase validated by the scientific community.

(2) .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. (c) Nuclear fusion is the main energy source for stars.

Describe what happens in nuclear fusion.

(3) .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. ..............................................................................................................................................

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*(d) Describe how the nuclear fission of uranium-235 is used to produce electricity in a nuclear power station.

(6) .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. ..............................................................................................................................................

(Total for Question is 12 marks)

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Q22.

Uranium-238 is an isotope of uranium. It may undergo either radioactive decay or nuclear fission.

A nucleus of uranium-238 is shown as Q in the chart.

(a) State two letters from the chart which show isotopes of the same element.

(1) .............................................................................................................................................. (b) Explain what happens when Q decays to P. (2) .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. (c) Explain what happens when P decays to O. (2) .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. ..............................................................................................................................................

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(d) Particles released during radioactive decay can have different energies.

A suitable unit for these energies is MeV. For one type of decay, the particles released have energies between 4.0 MeV and 10.0 MeV. The graph shows how far the particles with these energies travel in air.

(i) State the name of this type of particle.

(1) .............................................................................................................................................. (ii) Use information from the graph to describe how the distance travelled in air depends on the energy of the particle.

(2) .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. (e) Uranium-238 can only undergo nuclear fission by absorbing fast neutrons.

The fission emits neutrons which very quickly lose their energy.

Suggest why the fission of uranium-238 does not produce a chain reaction.

(2) .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. ..............................................................................................................................................

(Total for Question = 10 marks) Â 68 Â

Topic 6 – Benefits and drawbacks of using radioactive materials

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CHANGING IDEAS When radioactivity was first discovered in the late 1800s, scientists did not know it was dangerous: o Becquerel handled radioactive materials without any protection and suffered burns, but he did not realise that this damage was due to the ionising radiation o Marie Curie worked with radioactive materials all her life – her death from leukaemia (a type of cancer) was most likely the result of her not taking any precautions After these events, scientists began to link cancer and other health problems to the effects of ionising radiation…

We now know that a large amount of ionising radiation can cause tissue damage -­‐ e.g reddened skin (‘radiation burns’) Over long periods of time, ionising radiation can damage the DNA inside cells – this damage is called a ‘mutation’ DNA contains the instructions controlling a cell (i.e the genetic material)àwhen mutations occur, they can cause cells to malfunction, which can lead to cancer Handling radioactive sources: The risk of harm decreases with distance from the sourceàradioactive substances are always handled with tongs, and kept away from other people Protective clothing is worn in case the radioactive source happens to come into contact with the skin The most penetrating radiation (gamma rays) can be stopped by a sheet of lead àradioactive sources are kept in a lead-­‐lined container NUCLEAR WASTE Types of waste: The fission products from the uranium fuel used in nuclear power stations are very radioactive For the first 50 years – waste is called high level waste (HLW)…i.e it produces large amounts of ionising radiation For the next tens of thousands of years – waste is called intermediate level waste (ILW)…i.e waste is moderately radioactive o ILW includes metal cylinders that once contained the uranium fuel For the next tens of thousands of years after that – waste is called low level waste (LLW)…i.e waste is only slightly radioactiveàcan now be disposed o LLW includes clothing and cleaning materials from nuclear power stations o Hospitals are also a source of LLW because of the radioactive isotopes that are used in radiotherapy to treat cancer Storage and disposal of nuclear waste: HLW: o Transported inside thick concrete and steel containers, which absorb the radiation o The radioactive material is then stored in canisters and sealed in glass to prevent it from escaping ILW: taken out of canisters and sealed glass, but it is still stored inside concrete and steel containers LLW: once material is LLW it can be disposed of…3 options: o 1. Fire it into space – problem: launch vehicle could fall back to earth àspreading radioactive material everywhere o 2. Dump it in barrels in the sea – problem: barrels can corrode and release radioactive materials into the water o 3. Bury it in special landfill sites – this is the favoured method, but site of burial must be geologically stable (i.e have a very low risk of earthquakes) Advantages of nuclear power: Nuclear power stations themselves don’t directly produce carbon dioxide ànuclear power doesn’t contribute to global warming o (However, energy is needed to make some components of nuclear reactors àindirectly some carbon dioxide may be produced) 69

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Nuclear power is produced all the time (i.e not dependent on weather conditions) Nuclear power won’t run out for many years and it’s a very efficient process Disadvantages of nuclear power: Nuclear waste has to be stored for tens of thousands of years (i.e until the radioactivity has decreased to ‘LLW’) before it can be disposed… o During this time, if any of it leaks into the environment it can have serious effects on health – e.g tissue damage, cancer Some people think that nuclear power is unsafe because of the risk of accidents: o E.g in Chernobyl, 1986 -­‐ a nuclear power station exploded, spreading radioactive material across Europe HALF LIFE Recall (see Topic 5): o Radioactive substances have unstable nuclei that emit ionising radiation (alpha particles, beta particles and gamma rays) – this is a random process o As unstable nuclei emit ionising radiation, they lose (release) energy and decay to become more stable The ‘activity’ of any radioactive substance is the number of nuclear decays (i.e the number of unstable nuclei that emit ionising radiation and then become more stable) per second – it is measured in Becquerel (Bq) o 1 Bq is equal to one nuclear decay per second -­‐ the more unstable nuclei in a sample, the faster its rate of decayàthe higher its ‘activity’ The ‘half-­‐life’ is the time taken for the ‘activity’ for a radioactive substance to decrease by half (i.e it’s the time taken for half of the nuclei in a sample of a radioactive isotope to decay and become more stable) o The shorter the half-­‐life, the quicker the isotope decays The half-­‐life of a radioactive sample is found by recording its activity over a period of time -­‐ this is done using a Geiger-­‐Muller (GM) tube: o A GM tube is connected to a counter – every time ionising radiation is detected, it gives out a click o The ‘count rate’ is the number of clicks per second o The time it takes for the count rate to halve is the half-­‐life The half-­‐life can be calculated from a graph…e.g (on next page):

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o Activity of radioactive substance is initially 80 counts per second o It takes 6 days for its activity to reduce to 40…àits half-­‐life is 6 days BACKGROUND RADIATION We are constantly exposed to low levels of ionising radiation from space and from naturally radioactive substances in the environment -­‐ this is called ‘background radiation’ àWhen scientists measure the activity of a source… o They first need to measure the background radiation 70

The background radiation is then subtracted from measurements to give the corrected reading of the source’s activity Sources of background radiation: 1. Radon gas is the main source of background radiation: o When uranium in rocks decays, it produces other radioactive isotopes that also decay – one of these is radon o Radon diffuses into the air from rocks and soil and can build up in houses, especially if there is poor ventilation o The amount of radon in the air depends on the type of rock and its uranium content § àthe radon content (and so also the background radiation) varies according to where you are in the UK 2. X-­‐ray scans, gamma ray scans and radiotherapy treatment for cancer contribute to background radiation 3. Some foods naturally contain small amounts of radioactive substances Some background radiation comes from space…

4. High energy charged particles come out of stars, supernovae, neutron stars and black holes: o They are known as ‘cosmic rays’ and are a form of ionising radiation o Many cosmic rays are stopped by the upper atmosphere but some still reach the Earth’s surface USES OF RADIATION Diagnosis of cancer: Gamma rays can be used to help diagnose cancer…: o A tracer solution containing a source of gamma rays is injected into the body o The tracer collects where there are areas of abnormal activity (i.e where the cancer is) o The gamma rays can then be detected using a ‘gamma camera’àany cancer that is present can be seen Why gamma rays are used: o Gamma rays are used for this because they are weakly ionising(àmost penetrating)àpass straight through the body, allowing them to be detected Treatment of cancer: Ionising radiation can be used to treat diseases such as cancer – this is known as radiotherapy Usually this is done by firing beams of gamma ray radiation at cancer cells, killing them Sterilisation of equipment: Before they can be used on patients, surgical instruments need to be ‘sterilised’ so that microorganisms (i.e viruses and bacteria) are killed The usual method is to heat them (as microorganisms are killed by the heat) Some instruments, e.g plastic syringes, cannot be sterilised using heat (as they would melt)àthey are irradiated with gamma rays o I.e gamma rays are fired at the plastic syringes – this kills any microorganisms present Irradiating food: All foods contain bacteria – these bacteria are what eventually cause all food to decompose (i.e to go off) Some types of bacteria can also cause food poisoning (e.g salmonella) Some types of foods (fruit, vegetables, fish and poultry) are irradiated with gamma rays to kill bacteria…: o This makes the foods safer to eat and also means that they can be stored for longer before going off o Irradiating the food also kills any pests (e.g insects) that may be in it Note: irradiating food does not make the food more radioactive (though some foods may already be radioactive to begin with) Smoke alarms: A smoke alarm contains a source of alpha particles – usually a radioisotope called americium-­‐241 A smoke alarm consists of an electrical circuit with an air gap between two electrically charged (one positive, one negative) plates…: o The americium-­‐241 source releases a constant stream of alpha particles, which ionise the air to give positive ions and electrons o The electrons are attracted to the positively charged plate, positive ions are attracted to the negatively charged plateàa small electrical current flows in the air gap between the plates o As long as the current flows, the alarm will not sound o

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When smoke gets into the air gap, the smoke particles absorb the alpha particlesàcurrent flowing across the gap decreases o When current drops below a certain level, the alarm sounds Note: a source emitting alpha particles is used because alpha particles are very ionising Checking thicknesses: Paper is made by squeezing wood pulp between rollers The thickness of the paper is controlled by a detector, which counts the rate at which beta particles pass through the paper…

When the paper is too thin… o Lots of beta particles penetrate the paperàdetector records a high count rate o A computer senses the high count rateàreduces the pressure applied to the rollersàpaper is made thicker When the paper is too thick… o Few beta particles penetrate the paperàdetector records a low count rate o A computer senses the low count rateàincreases the pressure applied to the rollersàpaper is made thinner Note: beta particles are used for this because they are moderately ionising àsome pass through paper and others don’t, depending on the thickness of the paper Tracers in the environment: To detect leaks in water pipes underground, a gamma source is added to the water…a GM tube follows the path of the pipe, measuring the levels of radiation: o Where there’s a leak, water flows into the surrounding earth o The levels of radiation at this point are higher o These higher levels of radiation are detected by the GM tube o àthe point where the water leak has taken place can be located and then fixed o

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Topic 6: Advantages and disadvantages of using radioactive materials

P2 Specification Physics for your future

RAG Current

Topic

P2.6 Specification statements Revised ü 1 2

3

6.1 Be able to explain what is meant by background radiation, including how regional variations within the UK are caused in particular by radon gas.

6.2 Know the origins of background radiation from Earth and space.

6.3 Be able to describe uses of radioactivity, including: a) household fire (smoke) alarms

b) irradiating food

c) sterilisation of equipment

d) tracing and gauging thicknesses

e) diagnosis and treatment of cancer 6.4 Be able to describe how the activity of a radioactive source decreases over a period of time.

6.5 Know that the unit of activity of a radioactive isotope is the Becquerel, Bq. 6.6 Know that the half-­‐life of a radioactive isotope is the time taken for half the undecayed nuclei to decay.

6.7 Be able to use the concept of half-­‐life to carry out simple calculations on the decay of a radioactive isotope, including graphical representations.

6.8 Revise any investigations on models which simulate radioactive decay.

6.9 Be able to demonstrate an understanding of the dangers of ionising radiation in terms of tissue damage and possible mutations and relate this to the precautions needed.

6.10 Be able to describe how scientists have changed their ideas of radioactivity over time, including: a) the awareness of the hazards associated with radioactive sources b) why the scientific ideas change over time 6.11 Be able to discuss the long-­‐term possibilities for storage and disposal of nuclear waste.

6.12 Be able to evaluate the advantages and disadvantages of nuclear power for generating electricity, including the lack of carbon dioxide emissions, risks, public perception, waste disposal and safety issues.

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P2.6 Exam Questions – 41 marks, 41 minutes.

Q23.

Carbon-14 is a radioactive isotope that occurs naturally.

Scientists use carbon-14 to help find the age of old pieces of wood.

This technique is called carbon dating.

It uses the idea of half-life. (a) Which of these describes half-life?

Put a cross (

) in the box next to your answer.

(1)

A B C D

the time it takes for half of the undecayed nuclei to decay the time it takes for all of the undecayed nuclei to decay half the time it takes for all of the undecayed nuclei to decay half the time it takes for half of the undecayed nuclei to decay

(b) Sketch a graph to show how the activity of a radioactive isotope changes with time.

Use the axes below. Start your line from point P. (3)

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(c) A scientist investigates an old wooden comb.

The activity of the carbon-14 in it is 0.55 Bq. The estimated age of the comb is 11 400 years.

The half-life of carbon-14 is 5700 years. (i) Calculate the activity of the carbon-14 in the comb when it was new.

(3) .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. (ii) The scientist takes several readings of background radiation.

Explain why this is necessary to improve the accuracy of the investigation.

(2) .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. (iii) Old objects like the comb emit a very small amount of radiation.

The activity from the comb is about the same as comes from background radiation.

Scientists have stopped measuring the activity of carbon-14 for carbon dating.

Instead, they can measure the mass of undecayed carbon-14 left in the sample.

Suggest a reason for this change.

(1) .............................................................................................................................................. .............................................................................................................................................. ..............................................................................................................................................

(Total for Question is 10 marks) 75 Â

Q24. (a) A scientist uses a Geiger counter to measure the radioactivity of a sample.

She writes down the results in her notebook.

The Geiger counter gives a count rate of 120 counts per minute.

The average background radiation in her laboratory is 10 counts per minute. (i) What should she write down for the count rate of this sample?

Put a cross (

) in the box next to your answer.

(1)

A 12 counts per minute B 110 counts per minute C 130 counts per minute D 1200 counts per minute (ii) Name one source of background radiation.

(1) .............................................................................................................................................. (iii) Explain why some people are exposed to more background radiation than others.

(2) .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. (iv) Complete the sentence by putting a cross ( ) in the box next to your answer.

The recommended safe limit for exposure to radiation has been reduced over the last 80 years.

This is because now (1) A B C D

better instruments allow scientists to make measurements more quickly global warming has increased the rate of decay of radioactive materials humans release more radioactive materials into the environment scientists have a better understanding of the dangers of radiation 76 Â

(b) After the accident at the Fukushima nuclear plant in Japan, some drinking water became contaminated with radioactive iodine-131.

The graph shows how the activity of a sample of iodine-131 changes over two weeks.

(i) Use the graph to estimate the half-life of the iodine-131.

Show your working clearly.

(2)

.............................................................................................................................................. (ii) The recommended safe limit for a sample of this size is 100 Bq. How long did it take for the activity of the sample to decay until it was below the safe limit?

(1) .............................................................................................................................................. (iii) When iodine-131 decays, it emits beta radiation.

State one possible danger to health from exposure to beta radiation.

(1) .............................................................................................................................................. .............................................................................................................................................. ..............................................................................................................................................

(Total for Question is 9 marks)

77 Â

Q25. Radioactivity, its uses and problems (a) Radioactivity is used in medicine to diagnose and treat cancer.

State two other uses of radioactivity.

(2) .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. (b) Which of these is the correct definition for the half-life of a radioactive isotope?

Put a cross ( ) in the box next to your answer.

(1) A B C D

it is the time it takes for half of an atom to decay it is the number of atoms left when half have decayed it is the time taken for half the undecayed nuclei to decay it is half of the time it takes for all the undecayed nuclei to decay

(c) (i) Iodine-131 emits beta particles.

State what a beta particle is.

(1) .............................................................................................................................................. .............................................................................................................................................. (ii) The graph shows how the activity of iodine-131 varies with time.

A sample of iodine-131 has a mass of 100 mg.

How much iodine-131 will remain after 24 days?

(3) mass of iodine-131 = ...................................... mg 78 Â

(d) Scientists in Finland are building a facility for the storage of radioactive waste.

They plan to bury radioactive waste deep underground.

Describe some of the issues that need to be considered when planning to bury nuclear waste.

(3) .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. ..............................................................................................................................................

(Total for Question is 10 marks) Q26. (a) An underground oil pipe starts to leak oil.

To find the leak, a technician adds a gamma source to the oil flowing in the pipe.

Describe how the technician can find the position of the leak.

(2) .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. (b) Which of these is correct for half-life?

Put a cross (

) in the box next to your answer.

(1)

A B C D

It is half the time for all the atoms to decay It is the time it takes for an atom to half decay It is the time it takes for half an atom to decay It is the time it takes for half the atoms to decay

(c) The graph shows how the activity of a sample of a radioactive material changes with time.

The sample has an initial activity of 80 counts per minute.

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(i) Use the graph to find the half-life of the material.

(1)

.............................................................................................................................................. (ii) Another sample of the material has an initial count rate of 40 counts per minute.

Sketch, on the same axes, the activity of this sample for the first 4 days.

(2) *(d) Some scientists carry out an experiment to measure the radioactivity from a source to be used in a factory.

They measure the background radiation before and after their experiment.

They take the background count at the same place as they do their experiment.

Explain how this procedure helps to make sure that the results of the experiment are valid.

(6)

.............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. ..............................................................................................................................................

(Total for Question = 12 marks)

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Top ten tips Tip 1: Plan your revision Create a realistic and well-­‐presented timetable which you will adhere to. Include exam dates and deadlines for coursework. Add in sports/social/family commitments. Show it to your parents; get them to add in dates you might not know about.

If you have a block of exams, plan for them. If you have three exams in three days, you will need to be prepared to walk into the last exam before you walk into the first. For block exams create one page revision reminder notes which allow you to review the whole course in a short space of time.

Give priority to the exams which are worth the most to you, or you need to spend the most time on.

Tip 2: get a revision guide for your course Tip 3: print off all the past papers AND mark schemes possible. Use half the papers during revision, and half to test your knowledge throughout.

Tip 4: Contact your teacher so they can help when you get stuck Tip 5: get the right environment: o o o o o o

no distractions (no music, Facebook, tv, family and friends) not too hot (cold temperature keeps your body awake open a window if necessary) comfortable space or organisation (don’t get your papers all muddled up) paper to write notes pens/pencils

Tip 6: Segment your revision of a subject. Don’t try to revise all of the subject at once. Select one section, revise it, learn it, and find all the questions you can on that knowledge to test it.

Tip 7: Revise smart. Don't revise for more than your brain can cope with. You need to be aware of when it has stopped going in. I always found around 40-­‐50 mins hard-­‐core revision was the most useful time. Then take short useful breaks, use a different part of your brain, try doing something physical (don’t get onto blackops as you won’t get off it again). Take 10 minute breaks.

Tip 8: Nap!, believe it or not, you will boost the amount you can learn in one day by 30%+ just by taking short naps (10-­‐20 mins). Set an alarm though! This is because what you have learnt goes from your long term to your short term memory Tip 9: Don't think you know it, test it. Doing questions is the only way of testing your application of knowledge. This is easier in some subjects than others. Science and Maths there is no excuse for not doing loads of practise questions. Mark those questions using answers, check you have answer before even attempting questions as it will be useless otherwise.

Tip 10: follow my previous nine tips

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