10th Physics Notes English Medium

Page 1

2018

10th PHYSICS Short question answers. All questions from textbook are answered. All the questions from BISE Lahore PHYSICS paper from 2013-17 are answered with suitable picture diagrams. Exercise Short Questions All Questions from Past Papers

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Hamza Ayub STARS ACADEMY Shahdara Town Lahore 8/14/2018


U

nit 10

SIMPLE HARMONIC MOTION AND WAVES

10.1 What is simple harmonic motion? What are the necessary conditions for a body to execute simple harmonic motion? [2017#]

Simple Harmonic Motion: “SHM is such a vibratory motion in which net force is directly proportional to the displacement from mean position and is always directed towards the mean position.” Conditions: Acceleration must be directly proportional to displacement from mean position. Acceleration must be directed towards mean position. 10.2

Think of several examples of motion in everyday life that are simple harmonic.

Examples of SHM: • •

Motion of pendulum of clock. Motion of water particles forming waves.

10.3 What are damped oscillations? How damping progressively reduces the amplitude of oscillations?

Damped oscillations: “The oscillations of a system in the presence of some resistive force are called damped oscillations.” Reduced Amplitude: Friction reduces the mechanical energy of system which causes decrease in amplitude of oscillation. 10.4 How can you define the term wave? Elaborate the difference between mechanical and electromagnetic wave. Give examples of each.

Wave:

“Wave is a disturbance in the medium which causes the particles of medium to undergo vibratory motion about their mean position in equal intervals of time.”

1


Mechanical Waves: “Waves which require material medium for their propagation are called mechanical waves.�

Electromagnetic Waves: “Waves which require no medium for their propagation are called electromagnetic waves.� Example; Radio waves, X-Rays, Light waves

Example; Water waves, Sound waves. 10.5

Distinguish between longitudinal and transverse waves with suitable example. [2016, 17]

Longitudinal Waves: “In longitudinal waves, particles of medium move back and forth along the direction of propagation of wave.� Example; Sound waves, waves in slinky spring.

Transverse Waves: “In transverse waves, the vibratory motion of particles of medium is perpendicular to the direction of propagation of wave.� Example; Water waves.

10.7 Derive a relationship between velocity, frequency and wavelength of a wave. Write a formula relating velocity of wave to its time period and wavelength.

Wave Equation:

By definition;

If

Then

!" # $% & '( )

So

*

+

Hence,-./0123

45

6 7

8

+

10.8 Waves are the means of energy transfer without transfer of matter. Justify this statement with the help of simple experiment.

Energy transfer by Wave:Energy can be transferred by waves. We use our mechanical energy to make particles of string oscillating. Particles transfer this energy to the other and a wave is formed due to their oscillations. Hence waves transfer energy without transferring of matter. 10.9

Explain the following properties of waves with reference to the ripple tank experiment:[2016]

a.

Reflection

b.

Refraction

c.

Diffraction

Reflection: “When wave traveling from one medium falls on the surface of another medium, it may bounce back into the first medium. This phenomenon is called reflection of waves.�

2


Refraction: “When waves from one medium enter the second medium at some angle their direction of travel may change. This phenomenon is called refraction of waves.” Diffraction: “The bending of waves around obstacles or sharp edges is called diffraction of waves.”

10.10 Does increasing the frequency of a wave also increase its wavelength? If not, how are these quantities related? No! Frequency of wave and wavelength are inversely proportional to each other. According to wave equation 9: ; 4 <

= 5

So increase in frequency causes decrease the wavelength provided that velocity of wave remains same.

Some questions from Lahore Board: i.

Differentiate between amplitude and vibration with respect to SHM.

Amplitude:“The maximum displacement of an oscillating body on either side from its mean position is called its amplitude.” ii.

[2014,17]

Vibration:“One complete round of trip an oscillating body about its mean position is called one vibration.”

Define spring constant and write its unit.

[2013]

Spring Constant:“Ratio of force applied on spring to displacement produced is always a constant value which is called spring constant.” Unit: Unit of spring constant is >?@= . iii.

State Hook’s Law.

Hook’s Law: Hook’s law is stated as “Force applied on spring (stress) and change in its length (strain) is directly proportional to each other.” Mathematically:

A B C

3


iv.

Define mechanical waves and give example.

Mechanical Waves: “Waves which require any medium for their propagation are called mechanical waves.” Example: Water waves, Sound waves. v.

[2013]

Define frequency and time period.

Frequency: “The number of vibrations or cycles of a vibrating body in one second is called its frequency.” Time Period: “The time taken by a vibrating body to complete one vibration is called time period.” vi.

Define simple pendulum and write the formula for time period.

[2017]

Simple Pendulum: “A simple pendulum consists of small bob suspended by a light string, executing simple harmonic motion.” Time Period; D 2F G

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H

I

nit 11 SOUND

11.1

What is the necessary condition for the production of sound?

Conditions for Sound: Following are the necessary conditions for the production of sound; Sound is produced by a vibrating body. Sound travels through a material medium in form of compressional waves. 11.2 What is the effect of medium on speed of sound? In which medium sound travels faster: air, solid or liquid? Justify your answer.

Effect of Medium:Speed of sound is different in different media like gas, liquid and solid due change in space between molecules. Following is the trend showing speed of sound in different media J " ! K < J " MN < J "

4


11.3 How can you prove the mechanical nature of sound by a simple experiment? Sound travels in form of mechanical waves. We can prove it by experiment. Hang an electric bell in a jar, listen the sound of ringing bell. Now evacuate all air through vacuum pump and again ring the bell. From out you will see ringing bell, but listen no sound. There is no medium in the jar through which sound wave can travel to walls of jar and then your ears. 11.4 What do you understand by the longitudinal wave? Describe the longitudinal nature of sound waves. Longitudinal Waves:“In longitudinal waves the particles of the medium move back and forth along the direction of propagation of wave.” Longitudinal Nature of Sound:Sound travels in form of compressions and rarefactions in air. Due to change in air density, compressions and rarefactions are formed which move in the direction of wave. Hence it is clear that sound waves are longitudinal in nature. 11.5

Sound is a form of wave. List at least three reasons to support the idea that sound is wave.

Sound is wave: Following are some properties which show the wave nature of sound Sound is a disturbance which is transferred due to SHM of air particles. Soundmanifests the phenomena of reflection which is a basic property of waves. The wave equation 9: is applicable on sound. 11.6 We know that wave manifest phenomena of reflection, refraction and diffraction. Does sound also manifest these characteristics? Yes! Sound manifests all the basic properties of wave like reflection, rarefaction, diffraction etc. 11.7 What is the difference between loudness and intensity of sound? Derive the relationship between the two. [2016, 17] Loudness:“Loudness is the characteristic of sound by which loud and faint sounds can be distinguished.” It s not a physical quantity and is not measureable.

Intensity:“Sound energy passing per second through a unit area held perpendicular to the direction of propagation of sound wave is called intensity of sound.” Unit: Its units are O ?@P

5


11.8

On what factors does loudness of sound depend?

Factors affecting Loudness: Following factors affect the loudness of sound; Amplitude of vibrating surface: The loudness of the sound varies directly with the amplitude of vibrating body. Area of vibrating body: Loudness increases with the area of vibrating body and vice versa. Distance from vibrating body: The loudness of the sound varies inversely with the distance of vibrating body from the listener. 11.9 What do you mean by the term intensity level of sound? Name and define the unit of intensity of sound.

Intensity Level of Sound:“Intensity level of sound is the relative sound intensity at any point as compared to a standard sound intensity (Q/ ).” Units of Intensity Level:Unit of intensity level is ‘bel’. Definition:“If the intensity RSTof any unknown sound is 10 times greater than the standard intensity RSU T then intensity level of such a sound is 1 bel.” 11.11 What is difference between frequency and pitch? Describe their relationship graphically [2017#]

Pitch: “Pitch is the characteristics of sound by which we can distinguish between a shrill and a grave sound.” Relationship:The relationship between pitch is shown in figure. If frequency is low, pitch is low and vice versa.

Frequency: “The number of sound waves passing through one point in one second is called its frequency.”

11.12 Describe the effect of change in amplitude on loudness and the effect of change in frequency on pitch of sound.

Effect on Loudness: The loudness of the sound varies directly with the amplitude of vibrating body. The sound produced by a Sitar will be loud if we pluck its wires more violently. Effect on Frequency: Pitch depends on frequency. A higher pitch means a higher frequency and vice versa.

6


11.13 If the pitch of sound is increased, what are the changes in the following? a.

the frequency

b.

the wavelength

c.

the wave velocity

d.

the amplitude of the wave

a) Frequency: Increase in pitch means increase in frequency. b) Wavelength: Wavelength is decreased due to increase in frequency. 6 7 < 7 < c) Wave velocity: Wave velocity is constant. (constant quantity) d) Amplitude: Amplitude of wave is independent of pitch (frequency).

= 5

11.14 If we clap or speak in front of a building while standing at a particular distance, we rehear our sound after sometime. Can you explain how does this happen? [2016]

Rehearing of Sound: This happens due to the reflection of sound from the surface. The sound which we rehear is called echo. 11.15 What is the audible frequency range for human ear? Does this range vary with the age of people? Explain. [2014, 16]

Audible Frequency range: The audible frequency range for normal ear is 20-20000 Hz. Variation due to age: For Children; 20-20000 Hz, For Old People; 20-15000 Hz. 11.16 Explain that noise is a nuisance. Noise is Nuisance: Noise is hazardous to our health as it has negative effects on us like

Hearing loss Sleep disturbance Aggression Hypertension High stress levels.

11.17 Describe the importance of acoustic protection. Acoustics Protection:“The method or technique used to absorb undesirable sounds by soft and porous surfaces is called acoustic protection.� Importance:By using the technique noise pollution can be reduced so it is has an important role. 11.18 What are the uses of ultrasound in medicine?

[2017]

Uses of Ultrasonic:

7


Ultrasonic waves are used to diagnose disease in different organs. Powerful ultrasonic waves are used to remove blood clots in arteries. Ultrasound waves are used to get picture of thyroid gland for diagnosis. Some questions from Lahore Board: i.

[2015]

What is reflection of sound?

Reflection of Sound:“When sound is incident on the surface of a medium it bounces back into the first medium. This phenomenon is called reflection of sound.” Echo: ii.

“The sound we hear after reflection is called echo.” What is difference between noise and pollution?

Noise: “The sounds with jarring effect on our ears are called noise.” iii.

[2014,15]

Pollution: “The presence of harmful substances in environment is pollution.” [2014]

Describe the safe level of sound.

Safe Level of Sound: Following 2 factors ensure the safe level of sound. Sound Level 85-90 dB Timing 8 hours iv.

Differentiate between pitch and quality of sound.

Pitch of Sound: “Pitch is the characteristics of sound by which we can distinguish between a shrill and a grave sound.” v.

[2013,14,17]

Quality of Sound: “The characteristics of sound by which we can distinguish between two sounds of same loudness and pitch is called quality.”

How sound is produced?

[2013]

Sound Production:Sound is produced when an object vibrates. Due to these vibrations, air density changes hence compressions and rarefactions are formed which move in the direction of wave. This disturbance travels through material medium.

vi.

What do you know about SONAR?

[2016]

SONAR: “The technique of using ultrasound waves for locating depth or objects on ocean floor is called SONAR.” SONAR means SOund Navigation AndRanging.

8


vii.

What is a stethoscope?

Stethoscope:Stethoscope is medical instrument works on transmission of sound. It consists of a chest piece (diaphragm) and transmission rubber tubes. Sound waves travel from chest-piece to rubber tubes and the towards listener’s ears. viii.

[2017]

Name the two characteristics of sound.

Sound Characteristics: Following are the characteristics of sound. Sound consists of compressional waves that transfer energy. Sound waves are longitudinal(mechanical) in nature.

U

nit12 GEOMETRICAL OPTICS

12.1 What do you understand by reflection of light? Draw a diagram to illustrate reflection at plane surface.

Reflection of Light:“When light travelling in a certain medium falls on the surface of another medium, a part of it turns back in the same medium. This is called reflection of light.” The diagram shows the reflection of light. 12.2

Describe the following terms used in reflection: Normal, angle of incidence, angle of reflection

Normal:“When light enters a medium, the perpendicular on the point of incidence is called normal.” Angle of Incidence:“The angle between normal and incident ray is called incidence angle.” Angle of Reflection:“The angle between normal and reflected ray is called reflection angle.” 12.3

State laws of reflection.

[2014, 17]

Laws of reflection: i. ii.

The incident ray, the reflected ray and the normal at point of incidence all lie in the same plane. The angle of incidence is equal to the angle of reflection.

9


12.4 Define refraction of light. Describe the passage of light through parallel-sided transparent material.

Refraction of Light:“The bending of light from its straight path as it passes from one medium into another is called refraction of light.� Explanation:The diagram shows the refraction of light. When light enters in a different medium it changes its direction. 12.5

Define the following terms used in refraction: angle of refraction

Angle of incidence

Angle of Incidence:“The angle between normal and incident ray is called incidence angle.� Angle of Refraction:“The angle between normal and refracted ray is called angle of refraction.� 12.6 What is meant by refractive index of a material? How would you determine the refractive index of a rectangular glass slab? [2014]

Refractive Index:“The refractive index ‘n’ of a material is the ratio of speed of light ‘c’ in air to the speed of light ‘v’ in the material.� Formula: 12.7

VW UX Y IZ [

' = VW UX Y IZ \

State the laws of refraction of light.

0

,

[2017]

Laws of Refraction: Following are the laws of refraction. i. ii.

The incident ray, the refracted ray and the normal at point of incidence all lie in the same plane. The ratio of the sine of angle of incidence ‘I’ to the sine of the angle of refraction ‘r’ is always equal to a constant.

12.8 What is meant by the term total internal reflection?

Total Internal Reflection:“When the angle of incidence becomes larger than the critical angle, no refraction occurs. The entire light is reflected back into the denser medium. This is known as total internal reflection of light.�

10


12.9

State the conditions of total internal reflection.

Conditions for T.I.Reflection: Following are the conditions for total internal reflection. The light rays should enter from denser to rare medium. The angle of incidence should be greater than critical angle. 12.10 What is critical angle? Derive a relationship between critical angle and refractive index of a substance. [2017#]

Critical Angle:“The angle of incidence for which the angle of refraction becomes 90° is called critical angle.” Relation:According to Snell’s law,

_`a [

] 9K! " ^ " _`a " s ' s ' K

" s ' s ' 90 " s ' 1 s '

1 "

= fK ! g"h 10 ijk@= l n m 12.11 What are optical fibers? Describe how total internal reflection is used in light propagation through optical fibers. [2013]

Optical Fibers: Optical fibers consist of hair size threads of glass or plastic through which light can be travelled. Total Internal Reflection through Optical Fibers: Light entering from one end of core strikes the core-cladding boundary at an angle (42°) greater than critical angle of glass (45°) and is reflected back into the core. In this way light is total internally reflected in optical fiber. 12.12 Define the following terms applied to lens: Principal axis

optical center focal length

Principal Axis:“Each of two surfaces of a spherical lens is a section of a sphere. The line passing through the two centers of curvatures of the lens is called principal axis.” Optical Center:“A point on the principal axis at the center of lens is called optical center.” Focal Length:“The distance between optical center and principal focus is called focal length.”

11


12.13 What is meant by principal focus of a lens

a) convex lens b) concave

Focus of Convex Lens:“The light rays travelling parallel to principal axis after refracting through convex lens meet at a point on principal axis called principal focus.” Focus of Concave Lens:“The light rays travelling parallel to principal axis after refraction through concave lens appear to come from a point behind the lens called principal focus.” 12.14 Describe how light is refracted through a convex lens?

Refraction through Convex Lens: Light is refracted as explained below. The ray parallel to principal axis passes through the focal point after refraction by lens. The ray passing through the optical center passes straight through the lens and remains undeviated. The ray passing through the focal point becomes parallel to principal axis after refraction by the lens. 12.15 With the help of a ray diagram, how you can show the use of thin converging lens as a magnifying glass.

Magnifying Glass: A converging lens can be used as magnifying glass when object is placed very close to it. It makes a virtual, upright and magnified image. 12.16 A coin is placed at the principal focus of a converging lens. Is an image formed? What is its nature? No! Any image will not form on the screen.

Reason: The converging lens does not form of any object placed on the focal point. 12.17 What are the differences between real and virtual and image?

Real Image:“A real image is formed by actual intersection of light rays after reflection or refraction.” A real image can be seen on screen.

Virtual Image:“A virtual image is formed by imaginary intersection of light rays after reflection or refraction.” A virtual image cannot be seen on screen.

12


12.18 How does a converging lens can form a virtual image of a real object? How does a diverging lens can form a real image of a real object?

Converging lens forms virtual image of object placed between F and C. Diverging lens always form virtual image of real object. 12.19 Define power of a lens and its unit.

[2016]

Power of Lens:“Power of a lens is defined as the reciprocal of its focal length in meters.” Unit: Unit of power of lens is ‘Diopter’. Diopter:“1 Diopter is the power of a lens whose focal length is 1 meter.” 12.20 Describe the passage of light through a prism and measure the angle of deviation. Light through Prism: From figure, incident ray PE making incidence angle 1 on P is refracted towards EF. This refracted ray EF makes an angle o with surface of prism and move towards the other side of prism where it is refracted out of the prism making an angle-. This emergent ray FS is not parallel to incident ray rather makes angle D with is called angle of deviation. 12.21 Define the terms resolving power and magnifying power.

Resolving Power:“The resolving power of an instrument is its ability to distinguish between two closely placed objects.” Magnifying Power:“The magnifying power is defined as ‘the ratio of the angle subtended by the image as seen through the optical device to that subtended by the object at the unaided eye.” 12.22 Draw the ray diagram for: Simple microscope

[2015] compound microscope

refracting telescope

13


12.23 Mention the magnifying power of following instruments: compound microscope

Simple microscope refracting telescope

Simple Microscope:p

qr q

1 s Y

X

Compound Microscope:t R 1 s T Xu

Xv

Xu

Telescope:t Xu 12.24 Draw the ray diagram to show the formation of image in normal human eye.

Human Eye: Human eye consists of a converging lens which makes a diminished image on retina. 12.25 What is meant by the terms nearsightedness and farsightedness? How can these defects be corrected? [2013, 17]

Nearsightedness:“The disability of eye to form a distinct image of distant object on its retina is called nearsightedness.” Correction: Nearsightedness can be corrected by using diverging lens which will diverge light rays before entering the eye. Farsightedness:“The disability of eye to form a distinct image of nearby object on its retina is called farsightedness.” Correction: Farsightedness can be corrected by using converging lens which will refract light rays towards focus before entering the eye. Some questions from Lahore Board: i.

What do you know about endoscope?

[2013,16,17#]

Endoscope:“Endoscope is a medical instrument used to explore the interior organs of body for diagnostic and surgical purpose.” Commonly used endoscopes are gastro scope, cystoscope and bronchoscope.

14


ii.

[2013]

What is meant by center of curvature?

Center of curvature:“A spherical mirror is a part of a sphere. The center of this sphere is called center of curvature.” iii.

Regular Reflection:“The reflection by smooth surfaces is called regular reflection.” iv.

[2014**]

How do you differentiate regular and irregular reflection?

Irregular Reflection:“The reflection by rough surfaces is called irregular reflection.” [2014]

State Snell’s law.

Snell’s Law: Snell’s Law is stated as “During refraction the ratio

v.

_`a

_`a [

is equal to refractive index of the second medium.” ijk 1 m ijk o

Concave Mirror:“A spherical mirror whose inner curved surface is reflecting is called concave mirror.” Both real and virtual images can be formed by concave mirror.

vi.

[2015,16]

Differentiate between convex and concave mirror.

Convex Mirror:“A spherical mirror whose outer curved surface is reflecting is called convex mirror.” Only virtual and erect image is formed by convex mirror.”

Write some uses of lenses.

[2015]

Uses of Lens: Following are the uses of lens vii.

Lenses are used in spectacles. Lenses are used in microscope. Lenses are used as magnifying glass. Lenses are used binoculars. Lenses are used in slide projector. Lenses are used in camera. What is a prism?

[2015]

Prism:“Prism is a transparent object with at least two polished plane faces inclined towards each other from which light is refracted.” Uses: Prisms are used in binoculars and periscope.

15


viii.

[2016]

Write the medical use of light pipe.

Light Pipe: Light pipes are used to illuminate the inaccessible places of body by the doctors. ix.

What are spherical mirrors?

Spherical Mirror:“A mirror, whose polished and reflecting curved surface is a part of a sphere, is called a spherical mirror.” Types: Concave and convex mirror are 2 types of spherical mirrors. x.

What is the pole of mirror?

Pole of Mirror:“It is the midpoint of the curved surface of spherical mirror.” It is also called ‘vertex’. xi.

What is difference between concave and convex lens?

[2017]

Convex Lens:“The lens which causes incident Concave Lens:“The lens which causes incident parallel rays to converge at a point is known as parallel rays seem to diverge from a point is convex or converging lens.” known as concave or diverging lens.”

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nit 13

ELECTROSTATICS 13.2

Describe the method of charging bodies by electrostatic induction.

[2013, 16]

Electrostatic Induction:“Electrostatic induction is a process of charging a conductor without any contact with the charging body.” Method: To charge a body, bring it closer to the charged body. Due to charge opposite charge will induce on its both ends. 13.3

How does electrostatic induction differ from charging by friction?

Electrostatic Induction: Opposite charge is induced on opposite end of body only by bringing it closer to the charged body.

Friction Method: Due to friction heat is produced which causes transfer of electrons between the bodies and both are oppositely charged.

16


13.4 What is gold leaf electroscope? Discuss its working principle with a labeled diagram. [2016]

Electroscope:“Gold leaf electroscope is a sensitive instrument for detecting charges.” Working Principal: Gold leaf electroscope works on the principle of ‘Electrostatic Induction’. 13.5 Suppose you have a glass rod which becomes positively charged when you rub it with wool. Describe how you would charge the electroscope positively negatively

Charge Positively: Electroscope can be positively charged by bringing a negatively charged rod closer to it. Charge Negatively: Electroscope can be negatively charged by bringing a positively charged rod closer to it. 13.6

With the help of electroscope how you can find presence of charge on a body?

Presence of charge: To check the presence of charge on the body bring it closer to uncharged electroscope. If Leaves show deflection the body is positively or negatively charged. Leaves show no deflection the body is neutral. 13.7

Describe how would you determine the nature of the charge on a body by using electroscope?

Nature of Charge: To check the nature of charge on the body bring it closer to a positively charged electroscope. If Divergence of leaves increases, the body carries positive charge. Divergence of leaves decreases, the body carries negative charge. 13.8

Explain Coulomb’s law of electrostatics and write its mathematical form.

Coulomb’s Law:“The force of attraction or repulsion between two point charges is directly proportional to the product of the magnitude of charges and inversely proportional to the square of distance between them.” Mathematical Form:A B

wxwy oz

17


13.9

What is meant by electric field and electric field intensity?

Electric Field:“Electric field is a region around a charge in which it exerts electrostatic force on other charges.” Electric Field Intensity:“Electric field intensity at any point is defined as the force acting on a unit positive charge placed at that point.” 13.10 Is electric field intensity a vector quantity? What will be its direction?

Vector Electric Intensity:Yes! Electric intensity is a vector quantity. Direction: Electric intensity of a unit positive charge is directed in the same direction as electrostatic force acting on it. 13.11 How would you define the potential difference between two points?

Potential Difference:“The energy supplied by a unit positive charge as it moves from one point to the other in the direction of the field is called potential difference.” Unit: Unit of potential difference is ‘volt’. 13.12 Show that potential difference can be described as energy transfer per unit charge between two points. Potential of point A = {|

Suppose that

Potential of point B = {} Potential Energy of charge at point A = M{| Potential Energy of charge at point B = M{} Then Energy supplied by charge on moving through A to B = MR{| − {} T

m-o 3 .1-

R{| − {} T /2-m21 . 144-o-m0w

13.13 What do you meant by capacitance of a capacitor? Define unit of capacitance.

[2013, 16]

Capacitance:“Capacitance is the ability of a capacitor to store charge.” Unit: Unit of capacitance is ‘farad’. Farad:“If one coulomb of charge given to the plates of a capacitor produces a potential difference of one volt between the plates of the capacitor then its capacitance would be one farad.”

18


13.14 Derive the formula for equivalence capacitance for a series combination of a number of capacitors. [2013]

For series combination; Q = Q1 = Q2 = Q3 V = V 1 + V 2 + V3 {

x y ₃ s s fx fy f₃

{

1 1 1 s s fx fy f₃

{ 1 1 1 s s fx fy f₃ =

v

=

=

=

8

x s y s ₃ 6 v

13.16 What is difference between variable and fixed capacitor?

[2013, 16, 17#]

Types of Capacitor: Following are different types of capacitors. Fixed Capacitor:“The capacitor whose capacitance cannot be changed is called as a fixed capacitor.” Examples: paper capacitor, Mica capacitor. Variable Capacitor:“The capacitor whose capacitance can be changed is called as variable capacitor.” Example: Capacitor having combination of fixed and movable plates. 13.17 Enlist some uses of capacitors.

[2016]

Uses of Capacitor: Following are the uses of capacitor

In transmitter for tuning In radio for tuning In receiver for tuning In table fan, ceiling fan, washing machine In tube lights In resonant circuits

19


13.18 Discuss one application of static electricity.

[2017]

Use of Static Electricity: Static electricity is used to paint car bodies. Car body is charged and spray particles are oppositely charged by charging the nozzle of spray machine. Charged spray particles coming out of nozzle form a fine distribution on the body and stick to it due to attraction of opposite charges. 13.19 What are hazards of static electricity?

Hazards of Static Electricity: Following are the hazards of static electricity Lightning: The phenomenon of lightning occurs due to a large quantity of electric charge stored in heavy thunderclouds. Fires or Explosions: Static Electricity is a major cause of fires and explosions at many places like petrol tank and aircraft surface. Some questions from Lahore Board: i.

How can you identify conductors and insulators by using electroscope?

Identify Conductors: To check weather an object is conductor or insulator, touch it with the disc of charged electroscope. If deflection of leaves decreases the object will be a conductor. If deflection of leaves remains unchanged the object will be an insulator. ii.

What is a mica capacitor?

Mica Capacitor: Mica capacitor is an example of fixed capacitor. Dielectric: Mica is used as dielectric inside two metallic plates. The folded plates are enclosed in a plastic case. iii.

Write any two properties of electric field lines.

[2017]

Properties: Following are the properties of electric field lines. These are the imaginary lines indicating the direction of electrostatic force. Electric field lines are directed from positive charge to negative charge. The spacing between these lines shows the strength of electric field. iv.

Write a brief note on electrostatic air cleaner.

Electrostatic Air Cleaner: Electrostatic air cleaner is used to relive the discomfort of allergy sufferers. The airborne particles become positively charged when they make contact with positively charged mesh. Then they pass through a 2nd negatively charged mesh which causes

20


the negatively charged particles to precipitate out. In this way high percentage of contaminants is removed from air. v.

[2017]

Define the unit of electric field intensity.

Unit of Electric Intensity: The SI unit of electric field intensity is NC-1. Definition:“If 1 C positive charge placed in an electric field, feels 1 N force acting on it then electric field intensity will be 1 NC-1 at that point of field.”

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nit 14

CURRENT ELECTRICITY 14.1

[2016**]

Define and explain the term electric current.

Electric Current:“The rate of flow of electric charge through a cross-section is called electric current.” In metals electric current is produced due to flow of negatively charged electrons. In electrolytes electric current is produced due to flow of both positive and negative charges. Formula:I = Q/t Unit: The SI unit of electric current is ampere A. 14.2

What is difference between electronic current and conventional current?

Electronic Current:“Current flowing from negative to positive terminal of battery due to the flow of electrons is called electronic current.” 14.3

Conventional Current:“Current flowing from positive to negative terminal of battery due to the flow of positive charges is called conventional current.”

What do you meant by the term emf? Is it really a force? Explain.

[2017]

EMF:“It is the energy supplied by a battery to unit positive charge when it flows through the closed circuit.” It is measured in volt(V). It is not a mechanical force rather it is a driving force for electric charges.

21


14.4

How can you differentiate between emf and potential difference?

EMF:“It is the energy supplied by a battery to unit positive charge when it flows through the closed circuit.”

14.5

[2015]

Potential Difference:“Potential difference across the two ends of a conductor causes the dissipation of electrical energy into other forms of energy as charge flow through the circuit.”

Explain Ohm’s law. What are its limitations?

Ohm’s Law:“The amount of current passing through a conductor is directly proportional to the potential difference applied across its ends, provided the temperature and the physical state of the conductor do not change.” Limitations: Temperature should remain unchanged. Length, surface area and volume should remain unchanged. 14.6

[2017]

Define resistance and its unit.

Resistance:“The property of a substance to oppose the flow of electric charges through it is called resistance.” Unit: The SI unit of resistance is ohm. Ohm:“When a potential difference of one volt is applied across the ends of a conductor and one ampere of current passes through it, then its resistance will be one ohm.” 14.7

What is difference between conductors and insulators?

Conductors:“Materials in which electrons can freely move so as to pass electricity are called conductors.” Examples: Metals and graphite.

14.8

[2013, 16]

Insulators:“Materials in which electrons cannot freely move so as to pass electricity are called insulators.” Examples: Diamond, wood, plastic

State Joule’s law and explain the energy dissipation in a resistance.

[2013, 17#]

Joule’s Law:“The amount of heat generated in a resistance due to flow of charges is equal to the product of square of current I, resistance R and the time duration t.” Energy Dissipation: During current flow, charges move from higher potential to lower potential and give energy. Due to collisions of charges (resistance) energy is converted to heat energy. This energy is equal toO Qz 2.

22


14.9

[2013, 16]

What is difference between A.C. and D.C.?

D. C:“The current that does not change its direction of flow is known as direct current or D.C.” Source: The source of DC is chemical battery.

A. C:“The current that changes its direction of flow is known alternating current or A.C.” Source: The source of AC is AC generator.

14.10 Discuss the main features of parallel combinations of resistors.

[2014, 15]

Features of Parallel Combination: Following are the main features of parallel combination of resistors In parallel combination voltage across each resistor is same. In parallel combination total current through the circuit is sum of individual currents through the resistors. Equivalent resistance can be found by using formula 14.11 Determine the equivalent resistance of series combination of resistors.

Equivalent Resistance: For series combination I = I1 = I2 = I3 V = V1 + v 2 + v 3 As So

V1 = IR1

,

V2 = IR2 V = IR1

V3 = IR3

, +

IR2

+

IR3

V = I (R1 + R2 + R3) V/I = (R1 + R2 + R3) V/I = Req = (R1 + R2 + R3) Hence equivalent resistance can be calculated by adding individual resistances. 14.12 Describe briefly the hazards of household electricity.

Hazards of Electricity: Following are the hazards of household electricity Electric Shock: By touching a damage insulation wire one can receive electric shock. Short Circuit: Short circuit can severally damage the devices or person.

23


14.13 Describe four safety measures that should be taken in connection with the household circuit.

Safety Measurements: Following safety measurements should be taken

Use fuse in circuits. Use the circuit breaker. Use the earth wire. All devices should be attached in parallel manner.

14.14 What is the advantage of connecting the equipments in parallel instead of series?

Advantage of parallel connection: Following are the advantages of parallel connection On connecting parallel, same potential differences is applied across all devices. Hence all devices are individually switched on or off. In parallel combination of resistors equivalent resistance is less than the individual resistances due to which more current can pass through the circuit. Some questions from Lahore Board: i.

[2013]

Which are methods to combine resistors?

Methods to combine Resistors: There are 2 methods to combine resistors 1) Series Combination: In series combination of resistors there is only one path for current flow. 2) Parallel Combination: In parallel combination there is more than one path for current flow. ii.

[2014]

Define resistivity.

Resistivity:“The resistance of one meter cube of a material is equal to its resistivity or specific resistance.” It is represented as ρ. Unit: The SI unit of resistivity is ‘ohm-meter’ (Ω ). iii.

Differentiate between electric power and kilowatt-hour.

Electric Power:“The amount of energy supplied by current in unit time is known as electric power.” Formula:

[2013,14]

Kilowatt-hour:“The amount of energy delivered by a power of one kilowatt in one hour is called one kilowatt-hour.” Formula: 1 kilowatt-hour = 1000 W x 1 hour

P = I2 R

24


iv.

[2015]

Describe the function of volt meter and ammeter.

Function of Voltmeter: Voltmeter is used to measure the potential difference across a circuit component. Function of Ammeter: Ammeter is a current measuring device. Note: Ammeter is connected in series while voltmeter is connected in parallel. v.

If 0.5 coulomb charge passes through the wire in 10seconds then calculate the current flowing. .[2015]

As given,

Charge flowing = Q = 0.5 C Time = t = 10 s Current Flowing = I = Q/t = 0.5/10 I = 0.05 A

vi.

Prove that P = I2R

Electric Power = ”

Proof: Here

[2015]

™ K ! ™" Kh š ˆ{ ��

So

”

As

{ S]

Hence

” Sz]

vii.

•H– [ H –U[—

˜

Â?

{ S{

Hence Proved!

What are ohomic and non ohomic devices?

Ohmic Devices:“Materials that obey ohm’s law, and hence have a constant resistance over a wide range of voltages, are said to be ohmic.� Non Ohmic Devices:“Materials having resistance that changes with voltage or current are non ohmic.� viii.

[2016,17]

Define ampere.

Ampere:“If charge of one coulomb passes through a cross sectional area in one second, then current is one ampere.� Mathematically

" ! J K = ›

= Âœ = Â

25


ix.

[2016]

What is the use of earth wire?

Earth Wire: Many electrical appliances have metallic casing which is connected to ground using the earth wire. This earth wire provides a safe route for current flow. During a short circuit, if a person touches the metallic casing, the current flows through earth wire instead of person. Hence the person is saved. x.

What is a thermistor? Write its uses.

Thermistor:“Thermistor is a resistor whose resistance changes with temperature.� Uses: Thermistor is used in such a circuit which is a sensor of temperature change. xi.

What is the SI unit of electric power? Define it.

Unit of Power: The SI unit of electric power is watt. Watt:“If one joule of electrical energy is supplied by electric in one second then electric power is one watt.� 1 š xii.

8 Â?

8

[2017]

What is difference between a cell and a battery?

Cell: A cell is a single unit that converts chemical energy to electrical energy. Battery: Battery is a combination of cells. xiii.

Calculate the resistance of copper wire having 1m length and 2mm diameter.

[2017]

As given Length = l = 1 m Diameter = d = 2 mm

; g F

H

Â&#x; ž

R3.14T

ÂŁÂ&#x;Ă—8¼Œ§ ¨ ž

Š

3.14 Ă— 10@ÂŞ Â&#x;

8

Resistance = R = ÂŤ | = R1.69 Ă— 10@­ T ÂŽ.8ž×8ÂĽÂŚÂŻ Resistance = R = °. Âą Ă— =²@Âł ´

26


U

nit 15 ELECTROMAGNETISM

15.1 Demonstrate by an experiment that a magnetic field is produced around a straight current carrying conductor.

Ampere discovered that when current passes through a conductor, a magnetic field is produced around it. Explanation: If magnetic needle is placed around this conductor at different positions, it will align along the direction of magnetic field. Also if we sprinkle some iron fillings on the cardboard around this conductor, they will align themselves in concentric circles. 15.2 State and explain the rule by which the direction of the lines of force of magnetic field around a current carrying conductor can be determined? [201617#]

Right Hand Rule: Direction of magnetic field around conductor can be determined by using right hand rule which is stated as “Grasp a wire with your right hand such that your thumb is pointed in the direction of current. Then curling fingers of your hand will point in the direction of the magnetic field.” 15.3 You are given an unmarked magnetized steel bar and a bar magnet, its north and south ends are marked as N and S respectively. State how would you determine the polarity at each end of the unmarked bar?

Bring a side pole of it closer to the north pole of another magnetic bar. If the other bar reflects, it will be a north pole of bar otherwise a south pole. 15.4 When a straight current-carrying conductor is placed in a magnetic field, it experiences a force. State the rule by which the direction of this force can be found out. [2015]

Magnetic force acting on a conductor can be determined by Fleming’s Left Hand Rule which is stated as “Stretch the thumb, forefinger and the middle finger of the left hand mutually perpendicular to each other. If the forefinger points in the direction of the magnetic field, the middle finger in the direction of the current, then thumb would indicate the direction of the force acting on the conductor”

27


15.5

State that a current-carrying coil in a magnetic field experiences a torque.

Torque acting on Coil: If a current carrying coil is placed inside the magnetic field it experiences a torque. Explanation: If sides PQ and RS of a rectangular coil are placed between opposite poles of magnet perpendicularly, and current flow through coil, then opposite magnetic force acts on each side of coil which causes its rotation. 15.6

What is an electric motor? Explain the working principle of D.C. motor.

[2013]

Electric Motor:“Electric motor (DC motor) is an electrical device which is used to convert electric energy to mechanical energy.” Working Principle: A current carrying coil placed inside the magnetic field experiences a couple and begins rotation. This is the working principle of electric motor. 15.7 Describe a simple experiment to demonstrate that a changing magnetic field can induce emf in a circuit.

Induction of emf: According to Faraday, emf is induced in conductor due to relative motion of conductor and magnet (magnetic field). Explanation: Connect the two terminals of rectangular wire loop to galvanometer. Now move this loop, between poles of a strong magnet, perpendicularly. Due to this motion number of magnetic lines of force passing through rectangular loop changes hence emf is induced in circuit which is indicated by the deflection of galvanometer. 15.8 What are the factors which affect the magnitude of emf Induced in a circuit by a changing magnetic field? [2016, 17]

Factors affecting emf: Induced emf depends on following factors Speed of relative motion between coil and magnet. Number of turns of coil. 15.9 Describe the direction of an induced emf in a circuit. How does this phenomenon relate to conservation of energy? [2014, 17#]

According to Lenz’s Law;“The direction of an induced current in a circuit is always such that it opposes the cause that produces it.” Relation to Law of Conservation of Energy: If we apply the law of conservation of energy to electromagnetic induction, we realize that the electric energy induced in conductor comes from

28


the kinetic energy of moving magnet. We do mechanical work to move magnet which appears as electric energy. Hence process of electromagnetic induction is in accordance with the law of conservation of energy. 15.10 Draw a labeled diagram to illustrate the structure and working of A.C. generator.[2014, 15, 17#] Structure: AC generator consists of armature which is rotated inside the magnetic field. Working: When a coil is rotated inside the magnetic field, the value of induced current changes accordingly. This is the basic principal of AC generator. 15.11 What do you understand by the term mutual induction? [2013, 14, 16]

Mutual Induction:“The phenomenon of production of induced current in one coil due to change of current in a neighboring coil is called mutual induction.” 15.12 What is a transformer? Explain the working of a transformer in connection with mutual induction.

Transformer:“Transformer is an electric device which is used to increase or decrease the value of an alternating voltage.” Working Principle: Transformer works on the principle of mutual induction. 15.13 The voltage chosen for the transmission of electrical power over large distance is many times greater than the voltage of the domestic supply. State two reasons why electrical power is transferred at high voltage?

High Voltage Transmission: Following are the reasons for high voltage transmission of electricity Due to high voltage, transferring of electric power over long distances becomes easy. Due to high voltage, energy dissipation in the form of heat (heat =S ] ) is very low as current is low. 15.14 Why is the voltage used for the domestic supply much lower than the voltage at which power is transferred?

Low Domestic Voltage: Domestic machinery and household devices operate on low voltage (240 V). That is why voltage is lowered at sub city station to transfer it to domestic areas for use. Some questions from Lahore Board:

29


i.

What is difference between steps up and step down transformer?

Step-up Transformer:“If secondary voltage is greater than primary voltage, then transformer is called step-up transformer.â€? Âľ > ÂľW ii.

Step-down Transformer:“If secondary voltage is smaller than primary voltage, then transformer is called step-down transformer.â€? Âľ < ÂľW [2017]

Define electromagnet.

Electromagnet:“The type of temporary magnet, which is created when current flows through a coil, is called an electromagnet.� An electromagnet consists of iron core surrounded by current carrying coil. iii.

[2016]

What is meant by electromagnetic induction?

Electromagnetic Induction:“The production of an electric current across a conductor moving through a magnetic field is called electromagnetic induction.� Electric current is induced in electric generator due to electromagnetic induction. iv.

Write 2 methods to increase magnetic force on current carrying conductor.

[2017]

Increasing Magnetic Force: The magnetic force on conductor is increased if The current in conductor is increased. Strength of magnetic field is increased. Length of wire inside the magnetic field is increased.

U a)

nit 16 BASIC ELECTRONICS 16.1 Describe using one simple diagram in each case, what happens when a narrow beam of electron is passed through: A uniform electric field

b)

a uniform magnetic field

What do these results indicate about the charge on electron?

a)A uniform electric field: When electron beam passes through electric field it bends towards positive side which shows that electron has negative charge.

30


b)A uniform magnetic field: When electron beam passes through magnetic field applied by horse-shoe magnet, it is deflected from its direction. 16.2

Explain the working of different parts of oscilloscope.

[2016**]

Parts of Oscilloscope: Following are different parts of oscilloscope 1) Electron Gun: Electron gun is used to generate beam of electron. 2) Deflecting Plates: Deflecting plates used to deflect electron beam. 3) Fluorescent Screen: Fluorescent screen shows electron beam on the screen. 16.3

Name the uses of oscilloscope.

Uses of Oscilloscope: Following are the uses of oscilloscope 16.4

i.

To show waveform To measure voltage For range finding To find depth of sea To show heartbeat. Considering oscilloscope explain: How the filament is heated?

Heating Filament: Tungsten filament is heated by electricity. For this purpose current and voltage range is 0.3 A & 6 V respectively. ii.

Why the filament is heated?

Reason for Heating: Filament is heated to produce thermionic emission. i.

Why a large potential is applied between anode and cathode?

+ve Anode Potential: Greater the potential of anode, easier is to produce beam of electron. ii.

Why the tube is evacuated?

Reason for Vacuum: Vacuum is necessary to produce thermionic emission otherwise unnecessary canal rays will also produce with electron beam. 16.5

What is electron gun? Describe the process of thermionic emission.

[2017**]

Electron Gun: Electron gun is used to generate beam of electron.

31


Explanation of thermionic Emission: Tungsten filament is heated by electricity. For this purpose current and voltage range is 0.3 A & 6 V respectively. 16.6

[2017]

What do you understand by analogue and digital quantities?

Analogue Quantities:“Those quantities which change continuously with time or remain constant are called analogue quantities.” Examples: Pressure, temperature and time are examples of analogue quantities. Digital Electronics:“The quantities which change in non continuous steps are called digital quantities.” Note: Digital quantities are expressed in the form of digits. 16.7 Differentiate between analogue and digital electronics. Write down the name of 5 analogue and 5 digital devices that are commonly used in everyday life. [2016]

Analogue Electronics:“The branch of electronics which processes in the form of analogue quantities is called analogue electronics.” Analogue Devices:Old Radio, megaphones, volume control in old telephone. Digital Electronics:“The branch of electronics which processes data in the form of digits is called digital electronics.” Digital Devices:Computer, mobile phones, modern radios. 16.9

Write down some benefits of using digital electronics over analogue electronics.

Benefits of Digital Electronics: In digital electronics only two digits 1 and 0 are used and all data is delivered in form of these binary digits which is easy to process. 16.10 What are three universal Logic Gates? Give their symbols and truth tables.

[2013, 17#]

Logic Gates: Three universal logic gates are AND-gate, OR-gate and NOT-gate.

Some questions from Lahore Board:

32


i.

[2013,17]

What do you know about electronics?

Electronics:“Electronics is the branch of applied of physics which deals with the control of motion of electrons using electrical devices.” ii.

What is meant by DAC and ADC?

DAC:“A circuit which is used to convert digital signal to analogue signal is called as Digital to Analogue Converter DAC.” ADC:“A circuit which is used to convert analogue signal to digital signal is called as Analogue to Digital Converter ADC.”

U 17.1

nit 17

INFORMATION AND COMMUNICATION TECHNOLOGY

What is difference between data and information?

Data:“Facts and figures that are used by programs to produce useful information are called as data.”

17.2

[2017#]

Information:“In computer technology, processed data is called information.”

What do you understand by information and communication technology (ICT)?

[2017]

ICT:“Information and Communication Technology is concerned with the scientific methods and means to store and process vast amount of information instantly.” 17.3 What are the components of information technology? Clearly indicate the function of each component.

Components of IT: Information communication system is made of 5 components. 1) Hardware: The term hardware refers to machinery. It includes CPU, and all other equipment. 2) Software: Software is program and manual which contain instructions for hardware parts to produce useful information.

33


3) Data: Facts and figures that are used by programs to produce useful information are called as data. 4) Procedures: These are set of instructions and rules to design and use information system. 5) People: People influence the success or failure of information system. They use hardware, design software and write the procedures. 17.4

Differentiate between primary memory and secondary memory.

Primary Memory:“Primary memory is based on electronics and consists of integrated circuits.” It consists of 2 parts; RAM & ROM 17.5

Secondary Memory:“The data storage devices are generally the secondary memory.” It consists of hard disc, CD, DVD & flash drive etc.

Name different information storage devices and describe their uses.

[2016**]

Information Devices: Following are common information devices Audio, Video Cassettes: Audio and video signals are stored on these cassettes in form of magnetic field. Magnetic Disc: On magnetic discs data is stored in the form of binary digits, on the magnetic material. Compact Disc: In CD, digital data is stored using laser technology. Digital data is stored in the form of reflecting and non-reflecting spots called ‘lands’ & ‘pits’ respectively. A laser beam scans the surfaces and read the data. Flash Drive: Flash drive is a small device to store digital data. It consists of data storage ICs. It can be used to transport files from one computer to another. 17.6

Explain briefly the transmission of radio waves through space.

Transmission of Radio-waves: Radio-waves are used for satellite communication. A transmitter sends the signal to transmission channel. Radio-waves are continuously refracted by different layers in atmosphere and the signal is received by the receiver. 17.7

How light signals are sent through optical fibers?

Signal through Optical Fibers: Optical fiber is used as transmission channel to transmit light signals. Light enters in optical fiber such that incidence angle is greater than critical angle. In this way all light is reflected and light beam travels to the other end due to total internal reflection.

34


17.8

What is computer? What is the role of computer in everyday life?

Computer:“Computer is an electronic computing machine used for adding, subtracting or multiplying.” Role of Computer: Computer has an important role in our daily life. In offices computer is used for preparing letters, documents and reports. In hotels computers are used for advance booking, preparing bills and providing inquiry services. Doctors use computers for diagnosing illness and treatment of diseases. Architects use computers for building designing and city planning. Meteorologist uses computers for weather forecasting. Computers are used for designing, printing. 17.9

[2017]

What is difference between hardware and software? Name different software.

Hardware:“Hardware is part of computer that we can see or touch.” The term hardware refers to machinery. It includes CPU, and all other equipment.

Software:“Software is program and manual which contain instructions for hardware parts to produce useful information.” Commonly used software are WINDOWS, LINUX & Android etc.

17.10 What do you understand by the term word processing and data management?

[2013, 16]

Word Processing:“Word processing is such a use of computer through which we can write a letter, article, and book or prepare a report.” Data Management:“To collect all information for any purpose and to store them in the computer in more than one interlinked files, is called data managing.” 17.11 What is internet? Internet is useful source of knowledge and information. Discuss.

Internet:“Internet is a network of networks, which spreads all across the globe.” Useful: Teachers use the Internet to supplement their lessons, and a number of prestigious universities have opened up free online lectures and courses to everyone. It has even allowed retired teachers to read to and educate children in poorer countries. Widespread use of the Internet has opened up a substantial amount of knowledge to a much broader range of people than ever before. Some questions from Lahore Board:

35


i.

What is a hard disc?

Hard Disc:“A hard disc is a rigid, magnetically sensitive disc used as primary storage device in computers.” It spins rapidly and continuously in a separate box connected to computer. ii.

[2017]

Write two advantages of e-mail.

Advantages of e-mail: Following are the advantages of e-mail Fast Communication: We can send messages anywhere in world instantly. Simple use: After initial set-up email account it is easy to use. iii.

RAM:“RAM is abbreviation for Random Access Memory, which is used in computer as temporary memory.”

iv.

[2017]

Differentiate between RAM and ROM.

ROM:“ROM is abbreviation for Read Only Memory, which starts the computer.”

What is meant by operating system? Give an example.

Operating System:“Operating system is software that manages your computer and devices connected to it.” Example: WINDOWS, LINUX are commonly use operating system (OS). v.

[2017]

Write a note on fax machine.

Fax Machine: Fax machine is must for many businesses around world. A fax machine basically scans a page to convert its text and graphic to electrical signals and transmit it to other fax machine through telephone lines. Receiving machine convert the signal and print the copy of message that was sent.

U

nit 18 ATOMIC AND NUCLEAR PHYSICS 18.1 What is difference between atomic number and atomic mass number? Give a symbolic representation of nuclide.

Atomic Number:“The atomic number is equal to the number of protons in the nucleus.”

Atomic Mass Number:“The atomic mass number is equal to the number of nucleon in the nucleus.”

36


Representation of nuclide: A nuclide is represented by the symbol ¸·. Here A=atomic mass number & Z=Atomic number. 18.2 not?

What do you mean by the term radioactivity? Why some elements are radioactive but some are [2013]

Radioactivity:“Radioactivity is a phenomenon in which an unstable nucleus emits radiations.” Reason for Radioactivity: Subsequent experiments performed by Henry Becquerel suggested that radioactivity was the result of the decay or disintegration of unstable nuclei. While the stable elements do not emit radiations and are not radioactive. 18.3

How can we make radioactive elements artificially? Describe with a suitable example.

Artificial Method: Stable elements are made radioactive by the bombardment of neutrons. 8 ¥"

18.4

s ® 88µ! ¹ 88µ! º − K!

What are the three basic radioactive decay processes and how do they differ from each other?

Radioactive Decay: Basic radioactive processes are alpha-decay, beta-decay and gammadecay. Difference: Alpha-decay, beta-decay and gamma- decay are differ from each other as Alpha Decay: In alpha-decay parent element emits »-particle and atomic number decreases 2. Beta-Decay:In beta-decay parent element emits ¼-particle and atomic number increases 1. Gamma-Decay:In gamma-decay parent element emits º-radiations and atomic number remains same. 18.5

Write the alpha decay process for ® ½8 ! . Identify the parent and daughter nuclei in this decay.

Decay Process: The equation of alpha-decay process for ® ½8 ! is as follows ® ½8 !

Parent Element: ® ½8 !,

¹ ®¥ ­½g s ¾ R» − J!K T

Daughter Element; ®¥ ­½g

18.6 Explain whether the atomic number can increase during nuclear decay. Support your answer with example.

Yes! During beta-decay, atomic number of parent element increases 1.

37


Example: 18.7

8 ªf

¹ 8 ¿µ s @8¥¼ + energy

What do you understand by half-life of a radioactive element?

[2017]

Half Life:“The time during which half of the unstable radioactive nuclei disintegrate is called half life of radioactive element.” Explanation: Half life of Radium-226 is 1620 years. It means that half of its sample will be converted to daughter elements by the end of 1620 years. In the next 1620 years, half of the remaining radium will decay, leaving only one0fourth the original amount of radium, and so on. 18.8

Is radioactivity a spontaneous process? Elaborate your answer with a simple experiment.

No! Radioactivity is not a spontaneous process. It is a random process and the rate of radioactivity is directly proportional to the number of unstable nuclei present. 18.9

What is meant by background radiations? Enlist some sources of background radiations?

Background Radiations:“Radiations present in atmosphere due to different radioactive substances are called background radiations.” Sources: Radioactive elements on earth and outer space objects are sources of background radiations. 18.10 Describe two uses of radioisotopes in medicine, industry or research.

[2013]

Radioisotopes Uses: Cobalt-60 is used as nuclear medicine for cancer and tumors. In agriculture, radio phosphorus-32 is used as a tracer to find out how well plant is absorbing the phosphate fertilizer. 18.11 What are two common radiation hazards? Briefly describe the precautions that are taken against them? [2016]

Radiation Hazards: Radiations can cause Leukemia (cancer of blood cells). Radiations can cause Blindness or formation of Cataract in the eye. Precautions: The sources should only be handled by tongs and forceps. All radioactive sources should be stored in thick lead containers. 18.12 Complete this nuclear reaction:

®Á ½ À

8 ¹ 8 ¥ Á Â s ? s 2 ¥"

Does this reaction involve fission or fusion? Justify your answer.

Complete Reaction:

®Á ½ À

½® 8 ¹ 8 ¥ Á Â s ®­ÄK s 2 ¥" + energy

38


It is a fission reaction because a heavy nucleus is breaking into 2 nuclei with the release of energy. 18.13 Nuclear fusion reaction is more reliable and sustainable source of energy than nuclear fission chain reaction. Justify this statement with plausible arguments.

Arguments: On the basis of following reasons fusion reaction is preferred For fusion reaction raw material Hydrogen is easily available while for fission reaction necessary raw materials are expensive and laboriously available. In fission reaction, affordable energy is not possible due to chain fission reaction as compared to fusion reaction. 18.14 A nitrogen nuclide decays to become an oxygen nuclide by emitting an electron. Show this process with an equation. 8 ¿µ

Equation:

¹ 8 ­Å s @8¥

It is ¼-decay, atomic number increases 1 and nucleon number remains same. 18.15 Determine which of these radioactive decay processes are possible: a) b) c) d)

8 ­

®¥ ½¥Dℎ

®® ½8 ! 8 ªf

¹ 8 ­ s ¾

¹ ª ­­]! s ¾ ¥ ¹ ®® ½ À s @8¼

¹ 8 ¿µ s @8¥¼

Option ‘b’ & ‘c’ are possible decay processes. Some questions from Lahore Board: i.

What is neutron number?

Neutron Number:“The neutron number is equal to the number of neutrons in the nucleus.” Representation: Neutron number is represented by N. ii.

Define isotopes.

Isotopes:“Isotopes are the atoms of same element which have same number of protons but different number of neutron in their nuclei.” Example: Hydrogen has 3 isotopes protium ( 88¾ ), deuterium ( 8¾), tritium ( ®8¾ ). iii.

Define fission reaction.

[2017]

39


Fission Reaction:“Fission reaction is a process in which a heavy nucleus breaks into two nearly equal parts with the release of large energy.” Example: iv.

®Á 8 ¥" s ½ À

½ 8 ¹ 8 8 ÁªÇ! s ®ªÈK s 3 ¥" s " Kh

Write some properties of beta-radiations.

É-Radiations: Beta-radiations have following properties Beta-radiations consist of high energy electrons. Beta-radiations have less ionization power as compared to alpha-radiations. Beta-radiations have greater penetrating power than alpha-radiations while have lesser penetrating power than gamma rays. v.

Define radioactive isotopes.

[2017**#]

Radioactive Isotopes:“Artificially produced radioactive elements are called radioactive isotopes.” Example: Na-24 and P-30 are examples of radio isotopes. vi.

Define carbon-dating.

[2017]

Carbon Dating:“The age of live and dead objects can be estimated by comparing the activity of carbon-14 in them. This technique is called carbon dating.” Man has estimated the age of different ancient trees and rocks using the technique of carbon dating.

40


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