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Indenxowledge of the course Basic k
CHALLENGES THAT LEAVE THEIR IMPRINT Turn your bike into a mobile phone charger .......................................... 10
1 Computer-aided graphic design
.........................................................12
• The evolution of computer-aided design 1. View and perspective 2. Dimensioning 3. LibreCAD 4. Tinkercad 5. Tinkercad Codeblocks 6. Exporting files for 3D printing 7. OpenSCAD Technology workshop. Design a skatepark Understand, reflect and test your skills
2 Plastics manufacturing
.................................................................................... 54
• The materials we use to build our world 1. Plastic materials 2. Types of polymers 3. Manufacturing techniques for plastics 4. Introduction to 3D printing 5. Slicing software for 3D printing Technology workshop. Design and build a traffic light Understand, reflect and test your skills
3 Mechanic systems
...................................................................................................... 78
• What are machines used for? 1. Motion in mechanisms 2. Rotatory mechanisms 3. Mechanisms that transform motion 4. Machines and engines Understand, reflect and test your skills
Portfolio. ...................................................................................................................................................... 98
2
CHALLENGES THAT LEAVE THEIR IMPRINT Controlling noise pollution ........................................................................................... 100
CHALLENGES THAT LEAVE THEIR IMPRINT Programming a voice translator............................................................................180
4 Electric and electronic circuits
7 Digital devices maintenance and development of applications 182
.................................................... 102
• The unstoppable evolution of electronics
...................................................................................................................
1. Electrical components and symbols 2. Electric currents 3. Ohm’s law 4. Electric resistance 5. Series, parallel and mixed circuits 6. Capacitors 7. Electromagnetic relays 8. Measuring electrical quantities 9. Electrical energy and electric power 10. Electrical machines 11. Effects of electric current 12. Electronic receivers. LEDs Technology workshop. Electrical measures in a series circuit Understand, reflect and test your skills
5 Automatisms and control systems
• Use-optimised computer equipment 1. Operating systems 2. Operating systems maintenance 3. Windows maintenance 4. Developing applications with spreadsheets 5. Creating apps with App Inventor Understand, reflect and test your skills
8 Communications. Using the Internet safely • Communications for society
.......................................... 134
• From machines and electronics to intelligent robots 1. Control systems 2. Control systems elements 3. Transistors 4. Simple control systems Technology workshop. Motor speed controller Understand, reflect and test your skills
6 Programmed controlling with Arduino
........... 210
.......................... 154
• Maker culture: everything at the grasp of your hand 1. Programmed control with Arduino 2. Practising with Arduino Technology workshop. Make an ambient light sensor. Controlling a traffic light using Arduino Understand, reflect and test your skills
Portfolio. .....................................................................................................................................................178
1. 2. 3. 4. 5. 6. 7.
Communications over the Internet Digital identity Mobile communications Mobile phone services Risks and responsible use of mobile phones Security in information technology systems Emerging technologies and near future of communications Technology workshop. Setting up a safe Instagram account Understand, reflect and test your skills
9 The web and collaborative work
..............................................234
• The evolution of the web 1. 2. 3. 4. 5.
The web How the web works Web programming languages Collaborative work and publishing Developing a web page using a content management system 6. More Internet-sharing and distribution tools 7. Virtual meetings 8. What legal aspects about the Internet do you need to know? Technology workshop. Managing information on Drive Understand, reflect and test your skills
Portfolio. ................................................................................................................................................... 262
3
4
Electric and s t i u c r i c c i n o electr
THE UNSTOPPABLE EVOLUTION OF ELECTRONICS Research over the last two centuries has allowed us to master electricity, understand the nature of materials, and study atoms and the behaviour of their particles. As a result, we now have a huge range of electronic devices available to us with lots of different uses. Scientists have made incredible progress, and developments in electronics are now happening faster than ever before. It is impossible to imagine the pace of modern life without electronic systems and technology. Thanks to the development of devices, appliances and systems, we can instantly contact people on our smartphones, access the Internet, develop control systems, improve aviation and much more. The everyday uses of electronics are endless. The rapid growth of electronics has provided lots of opportunities and given us many advantages which have contributed to a better quality of life. However, our limitless desire for new technology results in the generation of millions of pieces of electronic waste every year worldwide. Some parts can be recycled, but others simply end up in landfill, leading to soil and water pollution. The cost of our need to have the
102
latest smartphone or TV is high, not just financially, but environmentally.
READING AND LISTENING
1 Are the following statements true or false? 1
Knowledge in physics that has grown over the last couple of hundred years has been key to our technological development.
2 How we fly hasn’t changed much since electronic systems appeared. 3 We can recycle most electrical devices and their parts, but some people choose not to.
2 What is the environmental cost of our love for technology?
3 Is the text hopeful? What is the opposite of hopeful? What suffix do we put on the end of the word ‘hope’ to make it the opposite of ‘hopeful’? Can you find two examples of words in the text with the same suffix?
SPEAKING
4 Organise a class debate around the
GES THAT
following statement: Electronic devices are killing our planet, we must stop ‘throw away’ culture. The class will be divided into three groups. Group 1: Environmentalists Group 2: Businessmen Group 3: Politicians
Follow the steps: 1 In your groups, outline your main arguments for or against the above statement. 2 Predict what the other groups might say and prepare your answers. 3 Have a class debate. Remember to be polite and listen to what others say. I understand your concerns, but from a business point of view… As a concerned environmentalist, I think it’s horrific that…
WRITING
5
6
1-2-4 The improvement and management of the treatment of electronic waste is closely linked to Sustainable Development Goals: 3, 6 and 11. In groups, search for information on: 1 How to correctly dispose of electrical devices. 2 Out of all the electrical waste we generate on a global scale, what percentage receives the proper treatment? And the percentage in Spain? 3 As a group, which measures would you implement to reduce this type of waste? Write a blog post for teenagers about technological waste and how you think we could improve how it is treated, or how we can change how we consume electronic devices.
CHALLEN
RINT
EIR IMP H T E V A E L
LEARNING SEQUENCE RAISE AWARENESS You will start off by making sure everyone is aware of the importance of designing energyefficient devices. Then you will investigate the cost of energy in your home! 1.1
Collect the data. Read you electricity meter every day for a week and note down the information in a spreadsheet. Calculate the daily and weekly cost of electricity in your home.
SAVE COSTS After analysing the data in activity 1, you probably assume that switching on a light to do your homework is very expensive. However, there are much more energy-efficient bulbs than conventional light bulbs on the market. 2.1 Investigate energy-efficient lighting. You will need to take into account energy use, and the lifespan and initial cost of the lamps to calculate how much you can save by using these devices. CONNECT ELECTRONIC COMPONENTS Get to know how to connect electronic components and measure electrical quantities. You will use breadboards, several different resistors and a multimeter. CHECK You will use LED lights to let you know whether the level of noise is low, medium or too high. You will determine LED lights’ polarity and set up circuits with them.
+ for more guidelines, go to anayaeducacion.es 103
1
ELECTRICAL COMPONENTS AND SYMBOLS
An electrical circuit is a closed path for electric charge to run through. It is made up of the following components: the source or generator of the electrical energy, control elements, electrical receivers or loads, protection elements and conductors.
1.1 The source of energy In direct current circuits the energy source is a chemical battery. Generators or plug sockets available in homes and industrial premises can provide alternating current, and the power supplied to these is provided by electricity companies. Element
Function
Symbol
Nonrechargeable battery
These produce electricity from chemicals. When the chemical products stop reacting, it stops producing energy. They have two metal terminals:
Graphic example
• A positive pole, or cathode. • A negative pole, or anode.
Battery
It generates electricity by using chemicals, similar to nonrechargeable batteries, but the process is reversible and it can be recharged a number of times.
Generator
This is a device that produces electricity from motion energy. The motion can be made by a combustion engine or other means.
Plug socket
G
A part that connects to the alternating current power grid. The connections on the wall are female and the plugs used to connect are male.
Understand, think, investigate… 1
104
Generate-Classify-Relate-Develop. There are different types of batteries, but they are all standardised. Make a table classifying the types of batteries that you normally use, including their dimensions and voltage value.
2 Why shouldn’t batteries be thrown away like normal rubbish? Where should we dispose of used batteries? Can mobile phone batteries and car batteries be recycled?
UNIT
1.2 Control elements Control elements allow you to connect and disconnect the circuit or some of its parts. Element
Function
Switch
A switch opens or closes the pathway for the current to flow through until it is pressed again.
Push button
This has a spring that returns the mechanism to its resting position. When we push it, we open (or close) the pathway of the current and when we release it, we close (or open) the pathway of electricity again.
Selector switch
This type of switch directs the pathway of the current through different circuits. The most common kind has two positions.
Symbol
Graphic example
Symbol
Graphic example
1.3 Electrical loads Energy receivers are also referred to as electrical loads, and they transform electricity into other forms of energy. Effect
Element
Light
A lamp, which can be halogen, low-consumption, fluorescent or incandescent. The latter options are no longer produced.
A fluorescent tube, which has a gas inside that is ionised and emits light when ignited by an electric shock.
Heat
It uses thermal components, such as a heat-emitting resistor, to heat the water in the tank.
Sound
A bell uses electromagnetism to create a rapid oscillating movement, making one metal part strike another.
Motion
A motor uses electricity and magnetism to move an inner part called a rotor that is affected by electromagnetic fields.
M
4
1
ELECTRICAL COMPONENTS AND SYMBOLS
1.4 Protection elements Protection elements are designed to protect the circuit from electrical overload or a short circuit. There are also devices that protect people and prevent them coming into contact with electrical energy. Effect
Element
Symbol
Fuse
A fuse has a metal wire which will melt if the current exceeds a certain value. When it melts, it must be replaced with a new one.
Circuit breaker
This is a device that opens the circuit automatically if the electrical current suddenly increases or exceeds a certain value. Once the incident has been resolved, it can be reset, not replaced like fuses.
Graphic example
I> I> I>
Residual current device
This automatically breaks a current when it detects a difference between the input and output current, preventing electric shock. They are found in our homes.
1.5 Conductors Conductors are metal elements, usually made of copper or aluminium, which transport electrical energy along a circuit. They are covered with a plastic material that serves as an insulator in order to* prevent accidents and unwanted electrical contact.
Understand, think, investigate… 3
What makes you say that? The diagram below shows a switched lamp in short assembly.
5 Find out the difference between a circuit breaker and a residual current device. Explain in your own words what each one is for and where they are installed.
6 European law prohibits the manufacture and
Where could it be interesting to assemble switched lamp circuits in a house? Why? Write your ideas in your notebook.
4 Where are protection elements located in a house or flat? 106
distribution of old incandescent lamps, and they are being replaced by energy-saving lamps and LEDs. Make a comparative table of features including average life, power consumed, luminosity and current price.
7 Have you thought about why electronic devices are not plugged directly into the mains?
UNIT
2
ELECTRIC CURRENTS Fundamental physical quantities There are seven fundamental physical quantities, all the others are derivatives. Electric current is one of them. Quantity
Unit
length
metre
mass
kilogram
time
second
electric current
ampere
temperature
kelvin
luminous intensity
candela
amount of substance
mole
4
Electric current is a physical phenomenon caused by the flow* of electric charges through a conductive material. In electricity when we talk about “current”, we are referring to the amount of electric charge, measured in coulombs (C), passing through a conductor for a specific time. In the international system, time is measured in seconds (s), so electric current should be measured in coulombs per second (C/s). This unit was renamed after the French physicist André-Marie Ampère, and so the unit of electric current is now called the ampere (A). Ampère made numerous discoveries about electricity and invented a current measuring device called the galvanometer. This led to the development of the ammeter, the instrument we now use to measure electric current. For electric current to flow between two points, there must be a difference in energy between them. This difference in potential, or potential difference, is also known as electric voltage and its unit of measurement is the volt (V). Voltage is the potential difference between two points if, when transporting a charge of one coulomb from one to the other, one joule of energy is consumed. To understand the concept of potential difference more easily, imagine that for a charge to transport electrical energy from one point to another, the amount of energy it has when it starts is higher than the amount of energy it will have at the end of the movement.
2.1 Direct current and alternating current There are two types of electric current: direct current and alternating current.
• Direct current is current that flows between two points without
Focus on English flow: a continuous, smooth movement of a gas, liquid or electricty along a path. in order to: a linking phrase we use to show the purpose of doing something, which is followed by the infinitive of a verb.
changing direction.
• Alternating current is current that circulates between two points and changes direction and value.
–
–
– +
+
+
–
+
–
+
+
–
Direct current
+
–
–
+ –
v
–
+
+
+
–
+
+
–
–
t
Understand, think, investigate… 8 Look for appliances that run on alternating current and others that run on direct current at home. Make a two-column table in your notebook to classify them.
9
I see, I think, I ask myself. Find out which type of electric current is used most often and find reasons why.
–
–
–
+
+
–
– +
+
+ –
+ –
+ –
+ –
– +
–
–
– +
–
+ +
+ –
– +
–
Alternating current
– +
–
– +
v
+
+
–
+
–
+
+
+
–
+
+
– +
–
+
t
–
107
3
OHM’S LAW
Georg Simon Ohm was a German scientist in the early 19th century. He discovered, through experiments in his laboratory, the relationship between the three fundamental electrical quantities: current, voltage and resistance.
V V I= R
Ohm’s law states that the current circulating in a circuit is directly proportional to the applied voltage and inversely proportional to the circuit resistance. The mathematical expression is:
V=I·R
I·R
I=
V R= I
To help you remember the formula of Ohm’s law, it can be represented graphically in the form of a triangle. As you can see, if you isolate one of the measurements, the position of the other two indicates the mathematical operation you need to apply.
V R
Where I represents the current measured in amps (A), V is the voltage or tension measured in volts (V), and R is the resistance measured in ohms (Ω). Electrical resistance is a property that all materials have and can be defined as the opposition they have against the flow of current. The unit it is measured in is the ohm, named in honour of Georg S. Ohm, and is represented by the Greek letter omega, Ω. The electrical resistance of an element or conductor depends on its physical characteristics and the material it’s made from. The coefficient of resistivity, a characteristic of each material, shows us how resistant a conductor of that material is at a given length and section. In this way, it is possible to calculate the resistance that a certain conductor will have by using the formula below: L A
R=ρ· Coefficient of resistivity: in green, conductive materials; in blue, semiconductive materials, and in brown, insulating materials.
Material
Where ρ is the coefficient of resistivity (expressed in Ω · m), L is the length of the conductor (expressed in m) and A is the area or section of the conductor (expressed in m2). The value of the coefficient of resistivity for different materials can be found in the table below:
Material
Scientific notation
Comparable figures
Steel
7,2 × 10-7
0,0000007200
Germanium
4,6 × 101
0,46
Silicon
2,5 × 103
2 500
0,0000000971
Granite
6 × 103
6 000
10,60 × 10-8
0,0000001060
Glass
1010
10 000 000 000
Tin
11,50 × 10-8
0,0000001150
Amber
5 × 1014
500 000 000 000 000
Lead
2,2 × 10-7
0,0000002200
Quartz
1017
100 000 000 000 000 000
Scientific notation
Comparable figures
Silver
1,59 × 10-8
0,0000000159
Copper
1,68 × 10-8
0,0000000168
Gold
2,35 × 10-8
0,0000000235
Aluminium
2,6 × 10-8
0,000000026
Tungsten
5,65 × 10-8
0,0000000565
Nickel
6,40 × 10-8
0,0000000640
Iron
9,71 × 10-8
Platinum
108
Resistivity at 22 °C (Ω · m)
Resistivity at 22 °C (Ω · m)
UNIT
4
Model example 1 We have a circuit powered by a 12 V battery and we know that it has a resistance of 3 Ω. What will the current be? If you cover the I in the triangle, you’ll see that V is above R, V R
so the formula you apply is I = Therefore, I = 12 V / 3 Ω = 4 A
2 Calculate the resistance of a copper conductor with a length of 10 km and a 5 mm2 cross section. The resistivity of copper is ρCu = 1.68 · 10-8 Ω · m. Datos:
ρCu = 1.68 · 10–8 Ω · m A = 5 mm2 = 5 mm2 · Solution
;
L = 10
Units
;
1 m2 = 5 · 10–6 m2 106 mm2
Substituting the data in the formula and performing the corresponding unit conversions:
=
1.68 · 10–8 · 10 000 5 · 10–6
Ω · mm2 resistivity of m aluminium is interpreted as meaning The 0.026
L R=ρ· A R = 1.68 · 10–8 Ω · m
The resistivity ρ has usually been 2 expressed in Ω · mm , which allows its m meaning to be interpreted in a simpler form than if Ω · m is used as unit.
10 000 m = 5 · 10–6 m2
Ω·m·m 1.68 · 100 Ω = 33.6 Ω = m2 5
that an aluminium conductor with a length of 1 m and a cross-section of 1 mm (a more common cross section than 1 m square) has an electrical resistance of 0.026 Ω.
Understand, think, investigate… Ω · mm2 are equal to one Ω · m? Do the m unit conversion step by step.
10 How many
11 Determine the resistance of a copper conductor with a 50 m length and 2 cm2 cross section. What would the resistance of the conductor be if it were made of aluminium?
12 In an electrical installation, the resistance of the conductors should not exceed 0.5 Ω. Calculate the minimum cross section of the copper conductor if the electrical load, or receiver, is located at a distance of one meter from the power source (think about the path of the conductor material from the source to the electrical load and then back to the source).
13 The resistivity of aluminium in Express it in Ω · m.
Ω · mm2 is 0.0282. m
14
Ideas pool. What happens to the resistance of a conductor in each of the following scenarios? a) We maintain its dimensions and change the material. b) We double its cross section. c) We triple its length.
15 The
inverse measurement of resistivity is conductivity. Using the table of resistivity values, calculate the conductivity of the materials in the table on the previous page. What unit will it be measured in?
16 How do you think the resistance of a conductor changes if it is twice as long? What if its diameter is reduced by half?
17 Convert the values of the resistivity table into the 2 unit Ω · mm . m
109
4
ELECTRIC RESISTANCE Variable resistors There are other types of resistors, such as adjustable resistors, which allow the user to set the value of the resistance as required. There are also components whose resistance varies according to other physical aspects, such as light, temperature, humidity, etc. These components are used as sensors that activate or deactivate the operation of the circuits.
Resistors are components used to regulate and limit the flow of current through the branches of electrical or electronic* circuits. In some cases, these components are used to generate heat from the circulation of the current, which is known as the Joule effect, and is used in heaters or irons. In the case of electronic circuits, the size of the resistors is very small. They are small cylinders, made of carbon or metal film assembled in a spiral on an insulator. They are covered with a protective ceramic layer with a heat dissipation capacity of no more than 1 watt. Coloured bands are engraved on the outisde to indicate the value of the resistor.
4.1 The resistor colour code If you want to know the value of a resistor, you need to look at the colours of its bands. In 4-band resistors, you will find three that are close to each other and a fourth that is further away or isn’t there at all. You should look at the group of three bands, starting with the one closest to the end of the resistor.
Variable terminal Terminal
Terminal
560 kX ± 5% 5
Resistive material COLOUR
Arrow or cursor
1ST BAND
LDR: a resistor that varies with light
5%
x10 kX
2ND BAND
MULTIPLIER
TOLERANCE
0
100
BROWN
1
1
101 = 10 X
± 1%
RED
2
2
102 = 100 X
± 2%
ORANGE
3
3
103 = 1 kX
YELLOW
4
4
104 = 10 kX
GREEN
5
5
105 = 100 kX
BLUE
6
6
106 = 1 MX
VIOLET
7
7
107 = 10 MX
GREY
8
8
WHITE
9
9
BLACK
Variable resistance
6
=1X
GOLD
0,1 X
± 5%
SILVER
0,01 X
± 10%
The coloured bands give the following information, reading them from left to right: 1st and 2nd band: these correspond to the two figures that give the resistance value. 3rd band or multiplier: this determines the power of 10 which the value obtained from the first 2 bands will be multiplied by. Its value is between –2 and 6, or 0.01 and 1 000 000.
Thermistor: a resistor that varies with temperature
110
4th band: this shows the tolerance. It indicates the percentage of variation that can exist between the theoretical value of the resistance and its real value. It allows us to calculate its maximum and minimum values. In the example next to the figure, we can say that the resistor has a value of 560 kΩ and a tolerance value of 5 %.
UNIT
4
Model example 1 Calculate the maximum and minimum values of a resistor with a nominal value of 3 300 Ω and 10 % tolerance. Solution The tolerance value indicates that the actual value of the resistance will be between the nominal value plus the tolerance and the nominal value minus the tolerance, for example: R = 3 300 Ω ± 10 %. The maximum value can be calculated by adding 10 % to the nominal value. Rmax = 3 300 Ω + 10 % · 3 300 Ω = 3 300 Ω + 330 Ω = 3 630 Ω The minimum, subtracting 10 % from the nominal value, in accordance with the tolerance will be: Rmin = 3 300 Ω − 10 % · 3 300 Ω = 3 300 Ω − 330 Ω = 2 970 Ω
Focus on English It can be confusing knowing when to use the words electric, electrical and electronic in English. We use electric to describe something that is powered by electricity, an electric oven, for example. We use electrical to describe something related to electricity, such an electrical engineer. And finally, something electronic is powered by electricity which passes through a component such as chip, resistor or transistor.
So, the real value of the resistance will be between 2 970 Ω and 3 630 Ω.
2 What is the colour code of a 3.3 KΩ resistor with 5 % tolerance? Solution To determine the colour code from the resistance value, it helps to write its value in a way that we can select the corresponding colour code directly from the table. You can do this by writing it as two digits multiplied by a power of 10. 3,3 KΩ = 3 300 Ω = 33 · 100 = 33 · 102 Once you have written the value like this, you only have to look at the corresponding colours in the table. 1st band 8 3 8 ORANGE 2nd band 8 3 8 ORANGE 3rd band 8 2 to the power of 100 8 RED 4th band 8 5 % 8 GOLD
Understand, think, investigate… 18 Calculate the nominal value and the tolerance of
19 What colour bands will the following resistors
resistors with the following colour codes:
have?
Strip 1
Strip 2
Strip 3
Strip 4
Brown
Green
Orange
Silver
Red
Red
Brown
Gold
Green
Blue
Black
Gold
Yellow
Violet
Green
Gold
47 kΩ ± 10 %; 33 Ω ± 5 %; 2 200 Ω ± 1 %; 6.8 MΩ ± 5 %; 390 kΩ ± 10 %; 0.1 MΩ ± 5 %
20
There are resistors that use five or six colour bands to indicate their values. Look for information about the use of these additional bands and find out what advantages they provide compared to those with four.
111
5
SERIES, PARALLEL AND MIXED CIRCUITS
The simplest electrical circuit is one made up of a battery, an electrical load a control element and conductors. This can be seen in the diagram on the left, in which there is no protection element. This is a typical circuit that can be assembled in a workshop with a 4.5 V battery, a flashlight bulb and a handmade switch made of paper clips and pins. Depending on how the elements of a circuit are connected, they are classified as series, parallel or mixed circuits.
5.1 Assembling series circuits
I + V –
R
A series circuit only offers one way for the current to flow. The elements are connected one after the other. Any type of component in a circuit can be connected in series: power sources, control elements and loads. In the picture on the left you can see that there are three batteries connected in series with two switches and four lamps. Each of the lamps has a certain resistance which can be measured.
S1 + –
V1
+ –
V2
+ –
V3
The total resistance of a series circuit is obtained by adding up the value of all the circuit resistances. In this case the resistance of each lamp.
S2
R1 I
R2 R3 R4
When several* generators or batteries are assembled in series, their polarity must be taken into consideration. If the positive pole of one battery is connected to the negative pole of the next one, the voltages are added together. If two poles of the same polarity are connected, they will cause the voltages to be subtracted (we should never do this). Connecting generators in series with the opposite poles connected allows for higher voltages in the circuits, without varying the values of the current. The table below outlines the specifics of a series circuit: Quantity
Explanation
Formula
Total resistance
The sum of the resistances making up the circuit.
Rt = R1 + R2 + ... + Rn
Voltage
The voltage provided by the battery is distributed among the different lamps, and the sum of the voltages of the lamps must be the same as the voltage of the generator.
V = VR1 + VR2 + ... + VRn
Since there is only one path for the current, it will be the same for all the elements in the circuit.
I = I1 = I2 = ... = In
Focus on English several: a quantifier that we use to describe a number of people or things that is more than a few but not a lot.
Current
Understand, think, investigate… 21 Draw an electrical circuit with four 1.5 V batteries assembled in series. After the positive pole of the first battery, add a switch.
112
After the switch, include three loads with a resistance of 1 Ω in series. The final load must connect to the negative pole of the last battery.
UNIT
4
Model example Calculate the current that runs through each resistor and its voltage Solution
R2 = 7W
I1
I2
I
In this case, Rt = R1 + R2 = 3 Ω + 7 Ω = 10 Ω.
+
Once we have calculated the total resistance and voltage of the battery, we can calculate the current of the circuit: I=
R1 = 3 W
–
10 V
10 V V =1A = 10 Ω Rt
Remember that this current is going to flow through both resistors, R1 and R2 because it is a series circuit. Therefore: I = I1 = I2 = 1 A To calculate the voltage using Ohm’s law, you need to know the value of the current flowing through each resistor, which you just calculated, and the value of each one of them. In this way, the voltage drop at the first resistor V1, will depend on I and on R1. V1 = I1 · R1 = I · R1 = 1A · 3 Ω = 3 V For the second resistor, we have: V2 = I2 · R2 = I · R2 = 1 A · 7 Ω = 7 V The sum of the voltage drops in both resistors must match the battery voltage: V = V1 + V2 = 3 V + 7 V = 10 V
Understand, think, investigate… 22 Draw an electrical circuit with four 1.5 V batteries assembled in series. After the positive pole of the first battery, add a fuse and a switch in series. After the switch, add three resistors in series with the following values: 1 Ω, 1.2 Ω and 1.5 Ω. The resistors connect through the opposite end to the negative pole of the last battery. Calculate the total values of V, R and I and the currents for each resistor in the circuit.
24 Calculate the total values of V, R and I corresponding to the circuit in activity 21 on the previous page.
25 Look at the reading of the ammeter and voltmeters in the circuit in the diagram below. Work out the value of the resistance R3, the voltage drop at the resistance R2 and the voltage provided by the battery.
23 Calculate the R3 resistance value the circuit below should have so that the current provided by the battery is 250 mA. What current circulates through resistors R1 and R2? + –
R1 = 10 W
–
R2 = 5 W
R3
1,8 V
V
V
R1 = 6 W +
V = 4,5 V
1,8 V
R2 = 3 W
R3
V A 300 mA
113
5
SERIES, PARALLEL AND MIXED CIRCUITS
5.2 Assembling parallel circuits A parallel circuit is one that has several possible pathways for the current to flow along. I I1 + –
V
R1
I2 R2
I3 R3
Two or more loads are said to be connected in parallel when both ends are joined to each other, allowing for the existence of as many paths for the current as* there are loads in the assembly. As each load has a measured resistance, if more than two loads are attached in parallel, we can calculate the equivalent or total resistance of the assembly. The following formula lets us find out the total resistance of a parallel circuit: 1 Rt = 1 1 1 + +…+ R1 R2 Rn When you have just two loads assembled in a parallel circuit we can find out the total resistance in a different way. This is a unique case where we can find the total resistance by finding the product of both resistances and then dividing this number by their sum. You can see this written in the following formula: Req =
Focus on English as many/much as: a quantifier to express the same amount of two different things.
If two or more generators are connected in parallel, we need to be sure of two things. All of them should have the same voltage and if they are components with polarity, all the positive poles should be connected on one side, and all the negative ones on the other side. By connecting two or more generators of the same voltage in parallel, the voltage stays the same but the charge and current that can be supplied are increased. Quantity
Explanation
Total resistance
This is calculated as the inverse value of the sum of the inverse values of each of the resistors in the circuit. If there are two resistors, a different formula can be used: the product of the two resistances divided by their sum.
Voltage
Current
114
R1 · R2 R1 + R2
Formula
Rt =
1 1 1 + + ... + R1 R2
The voltage that the battery provides is the same for all the elements connected in parallel.
V = V1 = V2 = ... = Vn
Current flows through each branch of the circuit, which will depend on each branch’s resitance. The total current, which is provided by the battery, will be the sum of all the currents flowing through the different branches.
I = I1 + I2 + ... + In
1 Rn
UNIT
4
Model example Calculate the voltage and the current that runs through each resistor Solution: +
If you know the voltage of each resistor and their resistance values, you can calculate the value of the current flowing through each branch: I1 =
V1 V 12 V =4A = = R1 R1 3Ω
;
I2 =
I2
I1
I
–
R1 = 3 W
R2 = 6 W
12 V
V2 V 12 V =2A = = R2 R2 6Ω
The current provided by the battery should allow 4 A to pass through the first resistor and 2 A through the second, then: I = I1 + I2 = 4 A + 2 A = 6 A You can reach the same result by dividing the voltage of the battery by the total resistance: I=
V 12 V =6A = Rt 2Ω
The resistance has been calculated in the following way: Rt = (R1 · R2) / (R1 + R2) = (3 · 6) / (3 + 6) = 18 / 9 = 2 Ω
Understand, think, investigate… 26 When we only have two resistors in parallel we
28 Write the formula you need to use to find out the
can use an alternative formula to calculate the equivalent resistance: R · R2 Rt = 1 . Work out the necessary steps to arrive R1 + R2 at this formula from the usual formula:
total resistance of two resistors of equal value connected in parallel.
Rt =
27
29 Calculate the total resistance in the following circuits, and the currents that flow through them.
1 1 1 + R1 R2 1,5 V
Intuition and deduction. The following circuits have errors that means they won’t work. Say what they are.
1,5 V 1,5 V
+ – – +
1,5 V 1,5 V
1,5 V
+ – +
R1 1W
R3 100W
R2 10W
–
+ – + –
R1 = 1W +
4,5 V
+ –
3V
+ –
R2 = 3,3W
4,5 V –
R3 = 4,7W
115
5
SERIES, PARALLEL AND MIXED CIRCUITS
5.3 Mixed circuits A mixed circuit is one that combines the characteristics of both series and parallel circuits. To solve a mixed circuit we need to reduce it to one of the two models we already know: a series circuit or a parallel circuit. To do this, we need to find out the equivalent resistance of those resistors that make up the circuit until a single resistance or total resistance is obtained.
Model example In the circuits shown below, what current is provided by the battery in each case? a)
R2 100 W
b)
R1 100 W
R2 100 W
R1 100 W R3 100 W
R3 100 W 9V+ –
9V+ –
Solution
Solution
a) We would start by calculating the equivalent value of the two 100 Ω resistors in parallel and continue as if it were a normal series circuit. After finding out the values of the parallel circuit, we can draw the following sequence of equivalent circuits:
b) First, we add up the two series resistors R1 and R2, and get a resistance of 200 Ω. Next we calculate the total resistance of the two 200 and 100 Ω parallel resistors, and we get a value of 66.66 Ω.
R1
R2 // R3
100 W
50 W
R1 + R2 200 W R3
9V+ –
9V+ –
Rt = R1 + (R2 // R3)
(R1 + R2) // R3
150 W 9V+ –
Finally, the total resistance is connected to a 9 V battery. Check that the current that passes through the generator is 60 mA by applying Ohm’s law.
116
100 W
66,66 W 9V+ – Check that the final value of the current of the battery is 135 mA. To get this result use Ohm’s law, just like in the previous example.
UNIT
4
Model example In the circuits on the previous page, what is the voltage drop for each element? Solution Continuing the two examples on the previous page, the generators here provide the circuit with a voltage of 9 volts. The voltage drop in each of the circuit’s elements is calculated by going through the sequence of equivalent circuits in the opposite direction, from the simplest to the most complex. So: a) Starting from the simplest equivalent circuit, we found the current value for the generator was 60 mA. Going back one step, we can see that the circuit is also equivalent with two resistors of 100 and 50 Ω, respectively. This shows that the potential difference of R1 can be found by applying Ohm’s law:
b) Starting from the simplest equivalent circuit we found a current value of 135 mA in the generator. Note that in the previous equivalent circuit the branch with the 100 Ω resistor and the branch with the 200 Ω resistor are in parallel with a 9 V battery and, therefore, the current flowing through each of them is: IR2/3 = 9 V/200 Ω = 45 mA
VR1 = 0,06 A · 100 Ω = 6 V
IR1 = 9 V/100 Ω = 90 mA
The remaining voltage needed to reach 9 V, namely 3 volts, will be the potential difference in both R2 and in R3, as both of them form a parallel:
The sum of these must be equal to the battery value, 135 mA. R1 + R2 200 W
VR2 = VR3 = 3 V 60 mA 9V+ –
6V
3V
R1 100 W
R2 // R3 50 W
135 mA
45 mA
9V
90 mA 9V+ –
R3 100 W
In the branch with resistors R1 and R2, the voltage distribution is made by applying Ohm’s law to each one of them: VR1 = 45mA · 100 Ω = 4.5 V
and parallel circuits ies ser of g din an rst de un r you n Strengthe tory circuit construction kit ra bo La al rtu Vi ET Ph e th h wit available at anayaeducacion.es. battery, resistors, switch, , ble (ca ts en pon com r you e oos Ch build your own circuits. d an s lue va ng rti sta e th e fin etc.), de to measure the voltage and Use the voltmeter and ammeter current of the circuit.
VR2 = 45 mA · 100 Ω = 4.5 V
117
6
CAPACITORS
A capacitor is an electrical component that stores charge due to electrical capacitance. Capacitance is formed in a capacitor when two conductive materials are separated by an insulator, or dielectric material. An electrical charge accumulates in each conductive material or plate when it is connected to the power supply. Each plate is charged with positive and negative polarity, respectively.
The capacitor symbol +
Polarised capacitor
Non-polarised capacitor
There is a different symbol for each type of capacitor.
Capacitance is measured in farads (F) and determines the amount of electrical charge per unit of voltage. This means that the capacitance C of a capacitor is 1 farad when, while it is subjected to a voltage V of 1 volt, it accumulates a charge Q of 1 coulomb. This can be represented by the formula: Q=C·V It’s not very common to find capacitors with capacitances as big as 1 farad. It’s more common for electronic circuits to use capacitors with smaller values between millifarads and nanofarads. Although many dielectric materials are used in capacitors, they can be classified into two basic types: polarised and non-polarised capacitors. Polarised capacitors have higher capacitance values but have the disadvantage of having a shorter life.
Capacitor behaviour
Capacitors according to the type of dielectric material Non-polarised capacitors +
– +
–+
–
Source of direct current
+
–
Source of alternating current
+
– +
–+
Polarised capacitors
Polyester
Electrolytic
Ceramic
Tantalum
–
Open circuit
+
–
Closed circuit
A capacitor behaves like an open circuit in the presence of a direct current. However, when it is subjected to alternating current, it acts almost like a short circuit.
Understand, think, investigate… 30 What capacitance in millifarads is equal to 4 700 microfarads?
31 Convert a capacitance of 220 nanofarads into microfarads.
32 Explain in your own words what a capacitor is and share your explanation with a partner.
118
33 Calculate what electrical charge a 22 millifarad capacitor connected to a 250 volts battery is able to store.
34 Look on the website of a capacitor manufacturer and list some types of polarised capacitors and their prices.
UNIT
7
ELECTROMAGNETIC RELAYS
4
A relay is a device used in electrical circuits as a signal-switching element. Unlike a breaker or a switch, it consists of two separate and isolated parts: a control circuit and a power circuit. A control circuit consists of two terminals connected to an electromagnetic coil or electromagnet. When current flows through it, a magnetic field is generated and changes the coil’s core into a magnet.
Solid state relays
Plastic protection
Electromagnetic coil
Common terminal
There are devices on the market that use silicon electronics rather than the action of a magnetic field as a switching medium. These are called solid state relays.
Coil core
Their advantage is that the power of the control circuit supports a wider range of values, between 5 V and 40 V. Electromagnetic relays, on the other hand, need a fixed working voltage to supply the coil with power.
Power circuit connections
M +4V
+ 12 V
–
–
Controlling signals with different natures Relays are suitable for when we have electrical signals of different natures, i.e. direct and alternating currents. Each one of them is used for different purposes. In the figure on the left we see a circuit diagram in which the relay activates an alternating current circuit.
230 Vca
Understand, think, investigate…
+4V – Manual control switch
Power circuit connections
It is common to use circuits with very low voltage and current consumption in order to control certain systems operating at high voltages and currents. In these installations, the relay acts as an intermediate control element to activate or disconnect everything in the power circuit. An example for this would be when starting a car.
R1
R1
Tilting piece or armour
Controlling signals with different measurements
Common terminal
Manual control switch
Connection terminal in magnetic attraction
A power circuit has three metal plates that act like the terminals of a switch. One of them, the intermediate plate, tilts and makes contact with an external plate. This depends on whether it is at rest or whether its position has changed due to the effect of the magnetic field.
Switching for power circuits
Control circuit coil
Idle connection terminal
35 Lamps
Do you know about the dispute between Edison and Tesla over controlling the distribution of electrical energy? Try to find information on the Internet by searching for ‘war of the currents’. Write a text that summarises what you find. 119
8
MEASURING ELECTRICAL QUANTITIES Analogue galvanometer
8.1 Ammeters, voltmeters and ohmmeters We need specific devices to measure electrical quantities. The first device used to make an electrical measurement was the galvanometer, although in reality, rather than measuring, it was used to detect the presence of electrical current. Its measuring board was later used in other measuring devices, such as the voltmeter, ammeter and ohmmeter. Today, all of them have been integrated into a single device, the digital multimeter. As you can see in the picture, in addition to the connection terminals, the multimeter has a numerical display and a selector dial which we use to select the electrical quantity we want to measure along with the appropriate scale. Display or numerical display
Power button
This serves mainly to detect electrical current. It has an analogue board with a measurement scale and a needle that will move in accordance with the quantity of the circulating current.
Scale for the ohmmeter function
Transistor socket
Continuity test Direct current ammeter function
Transistor gain measurement DC voltmeter function
Multimeter probes Alternating current ammeter function
AC voltmeter function
Transistor gain Unprotected high value current measuring port
Voltage and resistance measurement port
Fuse protected current measuring port
Common port
Before measuring anything, we need to check the connections so we don’t damage the device. The following guidelines should be followed: +
These probes are low resistivity wires equipped with specific terminals for measurement. In the photo, you can see the pointed terminals used to touch the circuit and measure the quantities. There are also crocodile terminals, which can be attached to different parts of a circuit.
120
–
A
Ammeter always connected in series with the circuit being measured
+ –
V
Voltmeter always connected in parallel with the circuit being measured
X
Ohmmeter always disconnected from the voltage source
UNIT Model example In the following practice you will learn how to check errors in your resistance measurements against the theoretical resolution.
4
Resistance naming structures I
R2
V3
Procedure Look at the circuit in the diagram on the right connected to a 4 V power source with the following resistances: R1 = 1 kΩ, R2 = 2 kΩ and R3 = 4 kΩ.
1 Work out the electrical resistance values on each resistor from the colour codes.
2 Work out the measurements of [I, V3] shown in the illustration. You should get the following values: RTOTAL = 2.8 KΩ 8 I = 1.42 mA 8 V3 = 1.16 V
3 Now check the data you get from making the physical circuit. To do this, measure each resistance with a multimeter. R1 = 1 kX
R2 = 2 kX
X
R3 = 4 kX
X
X
4 Copy the following table into your notebook and write down the measurement results for each resistance. Theoretical value Rt
Measured value Rm
Absolute error εa = Rt – Rm
Relative error εr = εa x 100/Rt
4V
+ –
R1
R3
As you may have noticed, electrical diagrams show us each resistance value. One characteristic of electronics is the use of very low electric current values in mA (milliamps) or even μA (microamps). This is because electrical resistors with high values of kΩ (kiloohm) or MΩ (megohm) are often used. To indicate these values in the diagrams, a very specific naming structure is usually used, consisting of placing a K or an M in the place of the separation of thousands or millions respectively. So, a resistance of 2 200 Ω, can be written 2.2K or 2K2, using the capital letter K. A resistance of 2 200 000 Ω, two million two hundred thousand ohms, can be written 2M2.
R1 R2 R3
5 Now assemble the circuit on a breadboard and connect the multimeter to take the electrical measurements indicated. R2
R2
R1
X
R3 4V
A +
Multimeter R1
R3
V
–
6 Copy the following table back into your notebook and calculate the errors obtained in the measurement. Theoretical value
Measured value
Absolute error εa = Vt – Vm
Relative error εr = εa x 100/Rt
RTOTAL I V3
7 Are any of the relative errors obtained in the tables greater than 5 %? If so, try to justify why the error was so high.
By using a multimeter, you can check the state of all points of a circuit. It is a delicate measuring device, despite its robust external appearance. You need to use it safely and in the correct way to take care of it.
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9
ELECTRICAL ENERGY AND ELECTRIC POWER
Generally speaking, energy is the ability that matter has to perform an action. In the case of electrical circuits, electrical energy allows the movement of charges between two points, identifying the difference in potential or voltage between those points. This formula can be written like the following example. E = (VA – VB)/Q
PCS A power control switch (PCS) is installed after the meter to control the maximum power contracted for the house, and make sure it is not exceeded.
Energy E is the potential difference between points A and B that each charge Q has. This will occur with all the charges that are transported between point A and B by transferring the energy E. The unit of energy in the International System is the joule (J). However, in engineering, where energy values are high, this unit is not typically used, but a more practical one, the watt-hour (Wh), is used. This is the same unit used in homes and industries to measure the energy consumed by electrical appliances and machinery. We can then work out what any appliance or machine has consumed in one month, for example 125 kilowatt-hours (KWh). Electrical power is also the amount of energy absorbed or generated by an element for each unit of time. Power and energy are related according to the formula below. E t
P=
However, specifically in electrical circuits (because voltage is a measure of energy per unit of charge, and the current is a measure of charge per unit of time due to the voltage), the product of both measurements will be the measure of power produced in that time. So, electrical power is the relationship between current in a circuit and the applied voltage, and is measured in watts (W). Here it is written mathematically in a formula. P=V·I Where P is the electrical power expressed in watts, V is the electrical voltage in volts and I is the current measured in amperes. By combining the above expression with Ohm’s law, we can find formulas that allow power to be calculated as a function of voltage and resistance or resistance and current.
Electrical power Look at how the measurements are related:
P
P = I2 · R
;
P=
V2 R
From the definition of power, we get E = P · t = V · I · t. To measure electricity consumption over a period of time, we use the Watt hour. Our household electricity bills use the multiple measurement kW. h or kWh.
I·V There are several equivalent units for watts: Watt =
122
Joule = volt × ampere Second
Value
Symbol
Name
103 W
kW
kilowatt
106 W
MW
megawatt
109 W
GW
gigawatt
UNIT
4
Model example The following problem comes from real data obtained from a house over a period of one month. The nominal power of a household appliance is indicated on its label, and the daily operating time is an estimate of the time it is running cumulatively throughout the day. To calculate the energy consumed, each data point from the power column must be multiplied by the corresponding operating time. As the units have been given in kW and in hours, the energy data point is indicated in kWh per day. To know the monthly consumption, we just multiply this number by 30 days.
Device
Rated power
Operating time
Power consumed in kWh/day
Power consumed in a month
Microwave
0.92
1.5
1.38
41.4
Set of lamps
0.4
6.4
2.56
76.8
Washing machine
2.5
1.2
3
90
Fridge
0.44
14
6.16
184.8
TV and sound systems
0.82
12
9.84
295.2
Constant consumption of other devices
0.8
24
19.2
576
Now think about the following questions. 1
If all the appliances are using their highest possible rate of consumption, how many devices can work simultaneously if we have 4.4 kW of power for a home?
2 What is the daily power consumption as a result? And the monthly one? 3 How much does the family spend per month if a kWh is charged at 0.11 euros?
Understand, think, investigate… 36
Find out what units are used to measure the output of an electric power plant.
37 Calculate the power used up by the resistances in the exercises from section 5 of this unit onwards.
38 Calculate the power of a light bulb which has a current of 0.25 A flowing through it when connected to a 230 V power source.
39 How much current flows through a 2 000 W hairdryer when connected to the 230 V AC mains?
40 How much energy is used up by a resistor with a maximum power of 1 W which has a current of 10 mA flowing through it and a voltage drop of 5 V over a period of 10 minutes? Give your result in joules.
41 A television has 100 W of power. In stand-by, it uses up 4 % of its power. Calculate the energy consumed over the course of a day if the television is on stand-by for 20 hours and is in operation for 4 hours. Calculate the daily and monthly cost of operation if the price per kWh before tax is 0.13 €.
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10
ELECTRICAL MACHINES
The British physicist Michael Faraday discovered that if a coil of conductive material moves within a magnetic field, it is capable of generating electrical current. The magnetic field is generated by using magnets or by making current flow through a different conductor. Machines that can produce electrical energy are based on this idea: one part is fixed in place and another part moves.
10.1 Electric generators
I
A dynamo is a machine capable of converting movement into direct current. Its main components are:
• Permanent magnets which generate the magnetic field.
S
• A coil of conductive material that, when spinning inside the magnetic field, generates the electric energy.
N
• Two electrical contacts called collectors on which the ends of the coil rest. This is where the electrical energy generated is collected. An alternator is a machine that is very similar to a dynamo, but which converts movement into the generation of alternating current. It also has two main components.
• An inductor, which is made up of permanent magnets or a series of electrically conductive coils which an electric current is passed through to create a magnetic field. Therefore, the inductor is the moving part of the machine and is located inside of it, rotating so that it produces a rotating magnetic field.
• The armature is the fixed, external part of the machine which houses the inductor inside of it. The armature is made up of a series of coils of conductive material that are affected by the rotating magnetic field of the inductor and on which electrical energy is induced, according to Faraday’s law. Since the amature coils are not moving, collectors are not needed. Instead, it has simple metal contacts which the electrical energy is supplied through.
Dynamo Direct current
Alternator Coil
Inductor
S Armature
Collector
N
N S Magnet
124
Brushes
Drive shaft
Alternating current
UNIT
10.2 Electric motors
4
Electric motor
Unlike dynamos and alternators, which use mechanical energy to produce electrical energy, electric motors do the opposite work and transform electricity into movement. There are motors that work with direct current and others that work with alternating current. In general, electric motors have high efficiency, around 75 %; that is, they transform 75 % or more of the energy supplied to them for their work. The main components of an electric motor are a stator and a rotor.
• Stator: This is where we can find the poles that will create magnetic
Stator
fields to make the rotor move. The number of poles of a motor is always even.
• Rotor: This is the moving part of the motor. The rotor is built around a metallic shaft, which is the part that transfers the circular movement due to the magnetic fields made in the stator.
Rotor
As we can see in the pictures, the construction of an alternator and that of a motor are very similar, although they have a few key differences.
Direct current motor
Alternating current motor
The current coming from the power supply circulates in through the rotor and the stator as they are connected. The main forms of connection between rotor and stator are in series, parallel or a compound form.
The current powering this motor is only used to power the reels or coils of the stator.
In order to direct the current to the rotor coils, it has brushes that are in contact with the bar commutator. This consists of the same number of pairs of diametrically opposed platens in the commutator as there are windings in the rotor. Current will only circulate through one coil, and this will be the coil whose bars are in contact with the brushes at that moment.
The rotor current will either be a spontaneous induced current, as in the squirrel-cage motor, or it will be supplied by a battery connection, as in other configurations. In this case it is called exciter current.
Fan Housing
Electromagnet
Stator
Armour Brushes
Feed
Shaft
Rotor Connection box
125
11
EFFECTS OF ELECTRIC CURRENT
One of the first scientific references to the effects of electric current comes from around 1775. The Italian scientists Luigi Galvani and Lucia Galvani, who collaborated with Alessandro Volta, connected a tin plate and then a silver coin to the muscle and the nerve of a frog’s leg, using copper wires. The frog’s leg suddenly contracted as if a life force had moved it. The Galvanis concluded that what moves living bodies is the force of ‘animal electricity’, which they called bioelectrogenesis. They had just used an accumulation of electrical energy, which Alessandro Volta had proposed by stacking metals to form an electric battery.
Heating effect applications
Today, we know much more about this electrical phenomenon and the effects that electrical currents produce in a multitude of devices that transform electrical energy into other forms of energy.
Heat is generated in stoves, irons and electric heaters by using electric resistors that release heat when current passes through them. It is also used as a means of protection in fuses inside devices. These melt when there is an overcurrent and prevent damage to electric circuits.
11.1 The heating effect The relationship between heat and electricity was proposed by James Prescott Joule, a 19th century English scientist, who quantified the energy that is used up in a conductor when electric current passes through it. When circulating, part of the kinetic energy of the electrons is transformed into heat, because these electrons collide with the atoms in the conducting material. The heating effect, also called the Joule effect, is the fundamental reason why electrical energy is transported at high voltages. When generating electrical power in power stations, it needs to be ensured that not too much energy is lost in the conductors when it is transported to where it will be needed and consumed. The distance between the two places is often hundreds of kilometres. When the transport voltage is raised to very high levels, it makes the electric current very small, so the amount of charge in movement is much lower. Consequently, there are less collisions between the charges and so the conductors are not overheated, minimising the loss of energy.
Production
Transformer station
Power plant
Step-up transformer
High voltage lines
Distribution
Industrial use
126
Agricultural use
Domestic use
Transformation centre
UNIT
4
11.2 The luminous effect Edison used this effect, closely related to the heating effect, to create the lightbulb. He practised creating a vacuum inside a glass bulb and arranged a carbon filament which electric current circulated through. The filament then turned incandescent, giving off light and heat. However, there are other electroluminescent phenomena that don’t give off heat, such as LED lamps. These lamps are made up of electronic devices called light-emitting diodes which have a composition based on arsenic and gallium. These convert the energy of the charges into a state that emits photons, the particles that carry light radiation.
11.3 The chemical effect Electric current causes chemical reactions when it passes through objects. This effect is used in electrolysis, which consists of submerging a pair of electrodes in a solution and making an electric current pass through them. One application for this is galvanisation (protecting steel from erosion by applying zinc). Electrolysis is used to break water down into oxygen and hydrogen, refine materials such as aluminium, and in anti-corrosive treatments.
11.4 The magnetic effect When current flows through conductors, it creates magnetic fields. We can check this out this by putting a compass next to a wire with electric current flowing through it. You will see that the needle stops pointing North and instead points perpendicularly to the wire. Because of this effect, we can build electromagnets for bells, electrically controlled door locks, relays, etc. We can often hear engineers and scientists referring to electromagnetism in their work, as these effects, electricity and magnetism, have a close relationship and they both come from natural forces. Thanks to the electromagnetic effect we have been able to set up communications by using electromagnetic waves, for example in radio, television, mobile phones or communications satellites.
11.5 The physiological effect The cells of living beings are externally protected by a membrane that isn’t very conductive, although they contain an electrolyte that it is a good conductor of electricity. We also know that animals’ nervous systems work with electrical impulses, so we can deduce that electric currents can alter how an organism functions. Electric current has been used to develop treatments for diseases, in the extermination of harmful viruses and the rehabilitation of muscular-skeletal injuries. There is a huge variety of medical and surgical devices which take advantage of the effects outlined above. However, one disadvantage of using electricity in medical and surgical devices is that they can cause electrocution or death by electrical discharge.
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12
ELECTRONIC RECEIVER. LEDs
12.1 LEDs The letters LED stand for light emitting diode. An LED is used as a luminous element but its behaviour is similar to that of a rectifying diode, meaning the electric current can flow through it if the voltage in the anode is higher than the voltage of the cathode. This circulation lets a large part of the electrons that go through the diode give off energy in the form of photons, which makes it luminescent. There is a large variety of LED models. LEDS are used for domestic lighting in light bulbs, in light-emitting elements in signs and advertising, in high resolution projection screens, and in traffic lights. This is because they consume much less electricity than older incandescent light bulbs.
LED terminals There are three ways to differentiate the terminals of an LED. If the diode still has the terminals it was made with, you will notice that one is longer than the other. The longest is the anode. If, on the other hand, the terminals have been cut shorter and do not have their original length, you have to look through the transparent capsule and you will see two geometric shapes: the post and the anvil. The post (smaller) is connected to the anode, whereas the anvil (bigger) is connected to the cathode. Transparent capsule
Post
Anvil
Anode +
Although they act as semiconductors, the main material in an LED is not silicon. Manufacturers use different chemical compounds to make them. An LED that lights up in red is made using aluminium gallium arsenide (AlGaAs), whereas blue LEDs are made from indium gallium nitride (InGaN). The colour of light emitted by LEDs depends on the wavelength of the light they emit. There is a range of signals that extend from 400 to 700 nanometres that make up the so-called visible spectrum or light in the electromagnetic spectrum. If a signal has a wavelength lower than 400 nanometres, it will be an ultraviolet light signal, whereas if its length is greater than 700 nanometres, it will be an infrared light signal. Both of these are invisible, like the signals emitted from remote controls. Look at the table below, it shows the characteristics of some of the most commonly used LEDs.
Cathode –
A third way to differentiate the terminals is by identifying the flat side section of the capsule, which is on the cathode side.
Colour
Average wavelength
Average voltage consumption
red
660 nm – 633 nm
1.8 V
orange
620 nm – 605 nm
2.1 V
yellow
595 nm – 574 nm
2.2 V
green
570 nm – 555 nm
3V
blue
525 nm – 430 nm
3.2 V
12.2 RGB LEDs Anode
128
Cathode
This type of LED is used in different ways and in a variety of applications, as it can emit a whole range of colours. The letters RGB stand for the initials of the additive colours: Red, Green and Blue. The most basic model on the market has a terminal for controlling the colour intensity of each one of the three additive colours and a fourth terminal used as a common cathode.
UNIT Guided practice
4
Structure of an RGB LED
Build a basic circuit for generating colours through an RGB LED. Notice in the assembly of this circuit that each active R, G and B terminal is connected to a potentiometer or variable resistor in a way that we can change the value of the voltage and the current that affects each terminal. The common terminal or cathode is connected to the negative pole of the battery through a protection resistor.
To get a better understanding of the RGB LED, we will think about it as if it were three LEDs placed together
This way, each one of the active terminals associated to each colour will connect to a certain voltage. To avoid the battery directly feeding one of the terminals when the potentiometer regulates to a non-existent value of resistance, we connect a small resistor of between 100 and 330 ohms in series with each potentiometer. This way we avoid breaking the diode as the result of connecting it to a high voltage. Another security measure is to use a battery or rechargeable battery no higher than 5 V.
Red terminal Common cathode
Blue terminal Green terminal
Active terminals Red Green Blue
Once you have built the circuit, move each one of the three potentiometers between its maximum and minimum value to check that the LED lights up with different colours. Practice using different positions on the potentiometers and then copy and fill in the table below in your notebook (Min = minimum resistance, Max = maximum resistance): Potentiometer position
Common cathode
However, check that this is the model you are going to work with.
RGB LED colour
Red
Green
Blue
Min
Min
Min
?
Understand, think, investigate…
Max
Min
Min
?
42 Draw the electrical diagram of the
Min
Max
Min
?
Min
Min
Max
?
Max
Max
Min
?
Min
Max
Max
?
Max
Min
Max
?
Max
Max
Max
?
circuit you built in the previous Guided practice activity in your notebook.
43
Think and share with a partner. The RGB LED model we have worked with has a common cathode, but diodes with a common anode are also available. Find out what the differences are between both types and draw an electrical diagram for each one. 129
P O H S K R O W Y G O L TECHNO PROJECT Presentation Components 1 breadboard 1 1 kΩ resistor 1 3.3 kΩ resistor 1 4.8 kΩ resistor 1 9 V battery 1 multimeter Black, red and green wires
STEP 1
Electrical measures in a series circuit A multimeter is a measuring device that you can use to measure different electrical values in a circuit. As you have seen in this unit, it has a knob on the front to select what you want to measure and the scale and its highest value. In this workshop, you are going to use a Tinkercad Circuit simulator to measure electrical resistance, current and voltage in a series circuit that has three resistors: R1 = 1 kΩ, R2 = 3.3 kΩ and R3 = 4.8 kΩ, with a tolerance of ± 5 %.
Measuring equivalent resistance In order to measure the equivalent resistance of a series circuit with these three resistors, you must first check that they are not connected to any power supply or battery.
Log in to Tinkercad Circuits with your username and build the series circuit on a breadboard. Turn the multimeter to the ohms setting. Read the measurement of the equivalent resistance and check that it is equal to the sum of the three individual resistors. Copy the following table in your notebook and write down the sum of the resistors under Expected value, and the multimeter measurement under Measured value. Compare the values. Expected value (kΩ)
Measured value (kΩ)
Equivalent resistance
STEP 2
130
Measuring current in the circuit You will have to add a battery or a power supply to the electrical circuit. As it is a series circuit, the current will only flow through one path, so you will have to turn the multimeter to the ammeter setting and connect it in series with the rest of the components of the circuit. Use a 9-volt battery from the components library.
UNIT
4
Calculate the expected current by using the correct formula and write it down in the first column. Then, write down the measurement you get when you use the simulator. Compare both values and decide whether it’s a reasonable measurement. Expected value (mA)
Measured value (mA)
Electric current
STEP 3
Measuring the voltages of the components in a circuit To measure the voltage of a component, remember to turn the multimeter to the voltmeter setting and connect it in parallel. Voltage
Expected value (V)
Measured value (V)
R1 R2 R3 Sum of voltages
Look at the connections for measuring the voltage at resistor R1 in the breadboard below. Write down the measurement in the Measured value column and repeat the procedure for resistors R2 and R3 by connecting the multimeter terminals in the correct places.
Then use the correct formula to calculate the voltage of each resistor. Write the information in the Expected value column. Finally, compare the values in the table and check that the sum of the voltages is equal to the voltage of the battery. 131
S THAT
E CHALLENG
RINT
IMP R I E H T E V LEA
9 Which of the three electrical resistors in the
UNDERSTAND
circuit below has the highest voltage? Which one has the strongest current flowing through it? Answer the questions without making any calculations and justify your answer. After the answer, make the appropriate calculations to prove your hypothesis.
Electric components and symbols
1 Draw the electrical symbols for the following elements: generator, switch (normally open), bell, lamp, battery and fuse.
2 How does a fuse act when there is excesive intensity in a circuit?
Electric current
3
5V
Before I thought…, now I think. Describe the differences between direct current and alternating current.
R1 = 5 kW
+ – R2 = 8 kW
R3 = 10 kW
Ohm’s law
4 What is the resistance of a copper cable 5 kilometres
10 Draw the circuit below in your notebook. Then, identify how many branches have a different current, and calculate the value of the current provided by the battery in milliamps.
long and 3 millimetres in diameter? How much would the resistance increase if a cable with half the diameter were used? And one made of aluminium?
5 What is the resistance of a circuit if a current of 50
R1 = 1,2 kW
R3 = 5,6 kW
R2 = 3,3 kW
R4 = 4,7 kW
milliamps is measured in the circuit when it is has a voltage feed of 12 V?
Electrical resistance
9V
6 Indicate the resistance values of the following resistors according to the colours of the bands.
11
7 A resistor has the following four bands: yellow, violet, yellow, gold. What are the maximum and minimum acceptable values on this resistor?
+ –
Copy the circuit below in your notebook. Then, write the value of each resistor next to it, noting that the coloured bands on each resistor are indicated in the table below. Once you have interpreted those values, calculate:
Series, parallel and mixed circuits
a) The total resistance of the circuit.
8
b) The current that the battery provides.
Preparing for the task. Look at the circuit below:
c) The voltage in the R1 resistor.
a) Calculate the total resistance and current that circulates through each section.
R1
b) If the resistor R2 in the circuit were short-circuited, what total resistance values would we get? R1 = 100 W
6V
R2 = 100 X
+ –
R3
R2
R4
Capacitors + 9V –
132
R3 = 100 W
R4 = 100 W
12
Ideas pool. Using the formula V = C · Q, where V is the voltage applied to a capacitor, C is the value of its capacitance, and Q is the charge value
Remember to select the work material from this unit for your portfolio.
UNIT
in coulombs that the capacitor stores, calculate the following situations:
15 Which unit on a multimeter would you use to correctly measure an electrical current of 12.4 milliamps from the options below?
a) The total resistance of the circuit. b) The current that the battery provides.
2 mA – 20 mA – 200 mA – 2 A
c) The voltage in the R1 resistor.
Electric energy and electric power
Electromagnetic relays
16 Calculate the monthly cost of using an induction cooker with an average consumption of 1.5 kW if it is used for 1 hour per day and electricity costs 0.11 €/kWh. Give your answer in joules and kWh.
13 Describe the operation of the following circuit containing an electromagnetic relay, considering that it can be operated from the manual switch. Which element works when the relay is not connected? What happens when the manual switch is closed?
R1 + –
4
12 V
+
14 V +
–
–
17
Think and share with a partner. A microwave with 1.2 kW of power has consumed 46.8 KWh of energy in a month of 30 days. What is the average time this appliance has been used every day?
Electrical machines
18 Draw an electrical diagram of the configuration of a DC motor and an AC motor. What is the main difference between them?
4V
19 What is the function of the armature in an alternator? And the inductor?
Measuring electrical quantities
14 Draw the diagram used to measure electrical current in a series circuit that contains two resistors of equal value.
Effects of electric current
20
Describe the physical phenomenon proposed by Joule, what it shows, and what its effects are.
REFLECT Reflect on your own learning, then share your answers about the challenge activities in groups. Download the complete table at anayaeducacion.es. Assessment descriptors
Totally achieved
Quite achieved
Roughly achieved
Developing
I can identify different electronic devices and connect them correctly.
…
…
…
…
I can build simple electrical circuits.
…
…
…
…
I am aware of the use of energy-efficient devices.
…
…
…
…
I can use ICT to present my ideas and have no difficulty doing so.
…
…
…
…
TEST YOUR SKILLS Go to anayaeducacion.es and use the self-assessment tools to check your progress. 133
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