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Physics
9th Standard
Chapter 10
LENS
Fill in the blanks
 A transparent material which is thicker in the middle and
thinner at the edges is called convex lens
 An object should be placed at twice the focal length in front
of a convex lens to get a real image of the size of the
object.
 The image of an object formed by a concave lens is virtual,
upright and diminished.
 An object is placed at a distance of 5cm from a convex lens
of length 10cm. The image formed is virtual and enlarged.
Q II
Fill in the blanks.
1 A ray of light passes undeviated after refraction from a
thin lens when it is incident at optic centre.
 Virtual, enlarged and erect image is formed on the same
side of an object in the convex lens. Then the position of
the object is between F and O.
 The distance between principal focus and the optic centre
of a lens is called its focal length.
Match the following
 The centre point of a lens
Optic centre
 Diverging lens
Concave lens
 The distance between principal focus
Focal length
And the optic centre of a lens
 The images caught on the screen
Real image
Answer the following
 What is lens?
 Lens is a piece of transparent material bound by two
surfaces of which at least one is curved.
 Define principal axis of a lens.
 The line passing through the optic centre of a lens and
perpendicular to the aperture is called the principal axis of a
lens.
 Define focal length of a lens.
 The distance between the principal focus and the optic
centre of the lens is called its focal length.
 What is the speed of light in vacuum?
 3x108 m/s.
 What is a real image?
 The image formed by the actual intersection of refracted
rays through the lens and which can be caught on a screen
is known as real image.
 How two converging lenses should be placed so that a
parallel beam becomes parallel after passing through two
lenses.
 Two lenses should be kept parallel to one another such that
the focus of the first is same point as the focus of the
second lens.
V] Answer the following
1. Write the differences between convex and concave lens
Ans
convex
lens
concave lens
a. it converges the light rays
a. it diverges the light rays
b. it is thicker in the middle
middle
and thinner at the edges.
b. it is thinner in the
and thicker at the edges.
2. Explain with a help of a ray diagram, why the convex lens
is also called a converging lens
Ans
For figure refer page no. 129
fig (c)
A convex lens refracts the parallel rays to converge at a point
on the principle axis. This refracted rays are called convergent
rays hence the lens is called converging lens.
3. Define the principal focus of a convex lens and that of a
concave lens
Ans. If all parallel rays passing through a convex lens
converge at a point that is called principle focus of convex
lens
If all parallel rays passing through a concave lens diverge
such that divergent rays appear come from a point on the
other side of the lens that point is known as principle focus of
concave lens
 An object is placed at a distance of 10cm from a convex
lens of focal length 20 cm. find the position and nature of the
image.
Ans.
u= -10 cm,
f= 20 cm
1/f = 1/V – 1/u
therefore 1/V=
1/f + 1/u
1/V= 1/20 - 1/10 = 1-2/20 = 1/20
V= -20 cm
The image is 20 cm away on the same side of the
object and it is virtual enlarged and erect
 An object is placed at a distance of 64 cm from white
screen. By placing a convex lens at a distance of 32 cm
from the object. It is found that a distance image of the
object is formed on the screen. Calculate the focal length of
the lens ?
Ans.
u= -32cm
V= 64 – 32 = 32 cm
1/f = 1/V – 1/u = 1/32 – (- 1/32)
1/f = 1/32 + 1/32 = 1+1/32 = 2/32
f = 32/2 = 16 cm
f = 16 cm
 A concave lens of 20 cm focal length forms an image 15
cm from the lens. Calculate the object distance.
Ans. 1/f = 1/V – 1/u
1/20 = 1/15 - 1/u
+1/u = 1/15 - 1/20 = 4-3/60 = 1/60
u = -60cm
 A convex lens of focal length 3 cm forms a real image at 24
cm from its optic centre. Calculate the distance of the
object from the lens.
Ans.
f= +3cm
V= 24cm
1/f = 1/V – 1/u
1/3= 1/24 – 1/u
1/u= 1/24 – 1/3 = 1-8/24
1/u= -7/24
u = -24/7 = 3.42 cm
u = 3.42 cm
 Complete the following ray diagram
For fig refer page no. 135
iv
figure
 Draw a ray diagram to show how a converging lens is able
to form the image of the sun
For figure refer page no. 129 fig 10.4
 An object is placed beyond twice the focal length of a
convex lens. Find the position nature and size of the image
with the help of a ray diagram.
For figure refer page no. 135 fig ii
Image is formed between F and 2F
Image is real, inverted and diminished
 Draw a diagram to represented the nature, position and
relative size of the image formed by a
 Convex lens for the object placed at 2F
 Concave lens for the object placed between F and 2F
 For figure refer page no. 135 fig iii
 For figure refer page no. 135 fig viii
STD-IX PHYSICS
CHAPTER-17
Circular motion
Answer the following
 Write the difference between revolutionary and rotator motion. Give an
example for each.
Ans: The type of motion in which a body moves in a circular path with the
change in its position is called revolutionary motion eg riding on a giant
wheel. Whereas in a top the body moves in a circular path about an axis without
change in its position is called rotatory motion. eg spinning top .
 A body moving in a circular path with constant speed is an accelerated
motion. Why?
Ans: A body moving in circular path with a constant speed has linear a
velocity which changes in direction at every moment .Therefore this motion
is called accelerated motion.
 Define centripetal force
Ans: Centripetal force is defined as the radial force directed towards the center
acting on
body in circular motion.
It is given as
F = mv2 /r
 Cyclist in a circular path leans towards centre .Give reason.
Ans: Cyclist in a circular path leans towards the center to attain the necessary
centripetal force.
 Give an illustration for centrifugal reaction.
Ans: Spinning of dryer in a washing machine . Due to centrifugal reaction or
inertia water particles fly away from wet clothes.
Give two applications of centrifugal force.
Ans: 1)A centrifugal governor is a device that controls the speed of an engine
by controlling the amount of fuel used. It works on the principle of centrifuge.
2) Water particles flying outside through the holes of the spinning drum
in a washing machine is due to centrifugal force.
Match the following
A
B
Ans
 Linear speed of a particle in
b) constant
a) rotatory motion.
a uniform circular motion.
 Centripetal force
d) towards the centre
 Spinning top
a) rotatory motion
 Electron revolving round nucleus
circular motion
b) constant
c) circular motion
d) towards the centre
c)
e) Linear motion.
.
 Fill up the blanks
 The force responsible for drying the clothes in a washing machine is
centrifugal force.
 Force involve in the uniform circular motion is given by mv2 / r.
 A cyclist moving in a circular path track leans towards the centre of the
circular path to gain necessary centripetal force.
 At any point in a circular motion the direction of the linear velocity of the
particle is changing
 The direction of centripetal force is towards the centre.
CHAPTER 16
OPTICAL
INSTRUMENTS
I] Fill in the blanks
1. The optical instrument used to view cricket match is ……….binocular
2. Telescope makes the far objects appear…………nearer
3. The type of lens which is used as simple microscope…….Biconvex lens
4. The final image in a compound microscope……. Virtual and inverted
5. Name of an optical instrument which is used to see erect image of
the distant object is………….. Terrestrial telescope
6. The type of lens used to make objective of an astronomical telescope
is………. Convex lens of larger focal length
7. The lens which is nearer to the object in a compound microscope is
Objective
8. The first telescope was designed by ………… John Lipper Shey
II] Match the following
1. Simple microscope
Virtual and magnified image
2. Compound microscope
and highly magnified
Real
image
3. Astronomical telescope
Virtual and lightly magnified
4. Binocular
Erect and magnified image
III] Answer the following briefly
1.
What is Telescope?
A. An instrument used to make distant object appear close to ones
eye
is known as a telescope.
2.
A.
Name the two types of microscopes.
i) simple microscope
ii) compound microscope
3.
What is a photographic camera?
A.
The instrument used to obtain permanent image of an object or a
scene is called a photographic camera
4.
Mention any 2 uses of simple microscope
A.
i) Used by watch repair and jewelers
ii) to read small letters
V]
Answer the following:
1.
Explain the working of a compound microscope.
A.
There are two lenses in a compound microscope. They are fitted
co-axially on the outer end of a cylindrical sliding tube. The lens of
smaller focal length is called objective lens and the lens of larger focal
length is called eye piece. A tiny object kept between F and 2 F of
the objective,is magnified and form real inverted image between F and
optic center of eye piece. This image is further magnified by eye piece
and forms a virtual erect image On the same side of the object This
image is highly enlarged.
2.
A. i)
Mention uses of binocular
Binocular is used to view cricket match.
ii) soldiers use binocular to observe enemy concentration.
3.
Write the differences between a binocular and terrestrial
telescope
A.
Terrestrial Telescope
Binocular
i) It has two total reflecting prisms
lens as a
between objective and eye piece
and a concave
i) A convex
objective
lens as the eye piece.
ii) This contain two telescope of
only one
ii) This contain
smaller size.
long telescope
4.
Explain the construction of an astronomical telescope.
A.
Take two cylindrical tubes such that one slides over the other. Fix
two convex lenses of different focal length at free ends. The
lens
of longer focal length is used as objectives and the lens of
shorter
focal length is used as eye piece. These two lenses can be
adjusted
according to the object or scenery to be seen clearly.
5. Give scientific reasons for the following
A. a) Focal length of the eye piece of a compound microscope is larger
------- the image formed by objective should be enlarge and to be
seen through eye piece, hence the focal length of the eye piece is
larger
b) A telescope of a binocular has two total internal reflecting
prisms
-------- total internal reflection prisms are used in binocular to
reduce
the size of the telescope. Otherwise we have to use two long
telescopes.
6. With the help of a labeled ray diagram show the formation of image
in
a) Simple microscope
b) Compound microscope
c) Astronomical telescope
a)
b)
c)
Refer page no 213
Refer page no. 214
Refer page no. 215
fig
16.2
fig 16.3
fig 16.5
7. Write the differences between a simple microscope and a compound
microscope
A.
Simple microscope
Compound Microscope
i. contains one lens
i. contains two lenses
ii) magnified image bigger
magnified image
ii) highly
than the object
is formed.
8. Write any two similarities between Astronomical and Terrestrial Tel -escope.
A. i. Both astronomical and terrestrial telescopes produce image of
distant object very near.
ii. Both telescopes are having sliding tubes the other.
Electricity
Q I
1
2
Choose the correct answer
electricity is a form of
energy.
Potential difference is also called
voltage.
3
Resistance of a wire is ‘ r’ ohms. The wire is stretched to double its length, thus its
resistance in ohms is
2r.
Q
II
Fill in the blanks

Electrica is a Latin world which means Static charge that develops when rubbed
against amber.

The smallest and lightest particle of an atom is the electron.

The S.I unit of electromotive force is volt.
Q III
Match the following
A

charge

Potential difference

Electric current

Resistance
Answer
Coulomb
Volts
Ampere
ohms
Q IV Answer the following

Write the difference between static electricity and electric current
Static electricity
current
Static charges remain at a
specified region.
current.

electric
Charges in motion is called
electric
Define electric potential
The work done in bringing a unit positive charge from infinity to a point in the
electric field is called the potential at that point.

What is electric resistance?
The property of a conductor to obstruct the flow of charges is called electrical
resistance.

Explain the term EMF
When there is no current in an electric circuit the potential difference between the
terminals of the source of emf itself is the electromotive force of that force

State ohms law.
Ohms law gives the relation between current and potential difference.
Ohm’s law
At constant temperature the current flowing through a conductor is
directly proportional to the potential difference across its en

What are various electrical hazards?
i)Electric fires may be caused by short – circuiting or overloaded electrical cables.
ii)Human body is good conductor of electricity. An electric shock is caused when the
current flows through the body to the ground.
iii)Even when an appliance is turned off ,but left plugged in with the switch on ,it can
cause
injury.


List out the various electric safety measures

It is important to unplug an electrical appliances when not in use.

Electrical appliances should be kept away from water sources.

Store the cords loosely coiled in a dry place.

Extension cords should not be in continuous use.

Electrical cords must be in good condition.

Connect plugs complete

Check that plugs fit properly into sockets.

Check the sparking lights near the sockets.
Explain the factors that affect electric resistance.

Material of the conductor ---- The molecular arrangement is different in different
substance, hence resistance depends on the material of the conductor.

Length of the conductor --- As the length of the conductor increases , the
obstruction of the conductor to the moving electron increases and thus the
electrical resistance also increases.

Thickness of the conductor --- As the thickness of the conductor decreases the
electrons get limited area to move. As a result of this resistance increases.

Temperature of the conductor --- The increase in the temperature is a measure of
increase in the vibrational energy of the atoms. W hen the temperature of a
conductor increases ,the atoms of the conductor obstruct the moving electron. As
a result the
resistance increases.
9
parallel.
Four resisters 5 , 6 Ω , 4 Ω and
8 Ω are connected in series and
Find the equivalent resistance in each case.
1
Diagram----------------------------------------------------
When the connection is in series
Rs = R1 +R2 +R3 +R4
Rs =
5+6+ 4+ 8=23Ω
When the connection is in parallel
Rp =1/R1 +1/R2 +1/R3 +1/R4
= 24+20+30+15 /120
= 89/120
Rp =120/89
= 1.348Ω
10 For the circuit given below , Calculate the equivalent resistance between the
points
P and Q
Resistance are in parallel
Rp = 1/R1 + 1/R2 +1/R3
= 1/7+1/8 +1/9
72+63+56 /504
=
191/504
Rp = 2.638Ω
2
Diagram------------------------------------------------
=
Resistance are in parallel
Rp = 1/R1 +1/R2
=
1/5+ 1/4
= 5+4 /20
=
9/20
=
Rp
20/9 =
=
2.22Ω
Between P and Q the resistance are in series
Equivalent series
= 504/191+ 20/9 =
4536+3820
/1719
=
8356/1719
=
4.861Ω
Electromagnetic
I
radiation
Choose the right answer

The speed of electromagnetic radiations in vacuum is -------
2
QII
Q III
3X 108
m/s
Infrared radiation are used in ------- long distance photography
Fill in the blanks

Electric and magnetic fields in electromagnetic wave are mutually perpendicular to each
other

The range of wave length of visible light is 4X10-7-7X10-7

The rays used to show bone structure is X – rays
Match
A
the following
B
1 Micro
waves
Hertz
2 Infra red radiation
William Herschell
3 X-rays
Willam Rontgen
4Gamma rays
Henry Becquerel
5Ultraviolet radiation
J.W.Ritter
Q IV
Answer the following
1 What is electromagnetic radiation?
Ans It is a wave energy consists of varying electric and magnetic fields mutually perpendicular planes.
This wave of energy propagates in the direction perpendicular to both electric field and magnetic field.
2. Draw a neat diagram of electromagnetic wave?
Ans
page no
263 fig 20.4
3 List the properties of electromagnetic wave ?
Ans i) All the electromagnetic waves in the electromagnetic spectrum travel at the speed
3x108m/s in
vacuum.
ii) They do not need any material medium for their propagation
iii) But in water or air the speed decreases because of absorption of some energy.
iv) Electromagnetic waves are three dimensional waves. They have dual nature such as particle
nature and wave nature.
v) different electromagnetic waves have different wavelengths and different frequencies.
Q4
Explain the electromagnetic spectrum with a neat diagram?
Ans Electromagnetic waves have a very wide range of frequencies and wave lengths .The orderly
arrangement of electromagnetic waves according to their frequency or wavelength is known as
electromagnetic spectrum. The entire range of electromagnetic spectrum is divided into different
regions. In different regions of the spectrum the electromagnetic wave is called by different name. Each
region of the spectrum overlaps the adjoining regions at both the ends. The range of wavelengths of the
electromagnetic waves varies from 10 2 m to 10-14 km.
For diagram refer page no 264
fig 20.5
Q 5 Write uses of the following
A a) Radio waves
- Radio waves are of wavelength range greater than 10-1 to 103. These waves
are used in radio broadcasting and in other communication system. Radio, T.V are working on these
waves.
b) Micro waves- these waves are like radio waves but having still shorter wavelength 1X10 -3.
Microwaves are also used for communication, mobile communication and in microwave oven etc.
c) Ultraviolet radiation - Wave length ranges of ultraviolet is 1X10-8 to 4X10-7m and frequency
range is 7.5 X1016Hz. These rays are used in hospitals for sterilization of surgical instruments. Ultraviolet
rays of shorter wavelengths are dangerous to our health but that of longer wavelength are useful in our
body in the manufacture of vitamin D. sun rays contain both short wave length as well as long
wavelength ultra violet rays.
d) X –rays – In hospitals Xrays are widely used. Fracture of bones can be found out using X rays
wavelength 1X10-11 to 1X10-8. X rays are used to locate foreign bodies such as bullets, pins, coins ets in
human body. For studying crystal, finding flaws in metals in industries, X rays are used. In the treatment
of tumours, cancer tumours. X rays are used “In Radiography”
e) Infra red radiation - The best use of infrared radiation is in solar equipments like solar cooker, solar
water heater, solar cells etc. In distance photography infrared radiation is used. Infrared radiation
stimulates blood circulation. In remote control this radiation is used.
f)Gamma rays - Gamma rays are used in the treatment of cancer. In gamma ray microscope. In
photoelectric effect and in gamma ray radiography Gamma rays used.
Gravitation
Q I
Choose the correct answer

Gravitational force is always -----attractive

Unit of acceleration due to gravity is

As the altitude increases the acceleration due to gravity

The relation connecting acceleration due to gravity and gravitational force is
GM/R2

S. I unit of gravitational constant is
ms -2
Nm 2 kg-2
decreases
g =

At the center of earth acceleration due to gravity is
Q II

zero
Fill in the blanks
The value of gravitational constant G=
6.67X10-11 Nm2 Kg-2

The acceleration due gravity is independent of mass of the object.

According to Newton’s law of gravity F= Gm1 m2/d2

In vacuum a coin and feather are released from same height at the same time then they will
reach the ground simultaneously.
Q III Answer the following

State and explain Newton’s law of gravitational force?
The force of attraction between any two bodies varies directly as the product of their
masses and inversely as the square of the distance between them.
If m1 m2 be masses of two bodies and r be the distance between them. If F be the
force of attraction then
F
m1
m2
and
The combination of these can be written as F=
OR
F
=G
m1
F
m 1 m2
m2
2
r
r2
G=6.67x 10-11 N m-2 Kg-2
G=Gravitational constant

Mention the effect of altitude and depth on the value of acceleration due to gravity.
Give the corresponding mathematical relation?
Ans ;
According to altitude or depth of the object from earth acceleration due to
gravity changes. If ‘M’ is the mass of earth, ‘R’ the radius of earth and ‘h’ the altitude
or height of the object then
g=
G M/(R+h) 2 when the body is on the surface of the
earth h = 0 and
g=
G M/R2. When height increases ‘g’ value decreases.
If the object is at a depth of ‘h’ below earth the value of acceleration due to
gravity
Increases i.e. g = GM/ ( R – h) 2 this value is greater than g = GM/R2. When
height
decreases ‘g’ value increases.

Describe the experiment of ‘ simple pendulum’ to find the value of acceleration due to
gravity
A
Arrange a simple pendulum. With a tape or meter scale, measure the length of the
pendulum from the base of the split cork to the centre of bob. Make the bob to
oscillate
such that the amplitude of the swing θ is approximately equal to 100 then measure
period of oscillation (T) for different lengths ( say h = 1m, 1.1m,1.2m,1.3) of the
pendulu
-m. find L/T2 for each length. Then using the formula g =4 L / T2 we can calculate
acceler
-ation due to gravity.
Iv

Solve the problem
A sphere of mass 10 Kg attracted by another sphere of mass 150 kg. When their
centers are separated by a distance of 0.28 m with equal to 1.3x10-6 N . Calculate
the gravitational constant.
F = 1.3x10-6
F = Gm 1 m2
d = 0.28m
d2
G = F x d2
m1 m2
G = 1.3 x 10-6
x 0.28 x 0.28
10 x 150
m1 =
10 kg
m2 =150 kg
= 1.3 x 10-6 x 0.0784
10 x 150
10-6 x 784
= 1.3 x
10 x 104 x 150
= 6.76 x 10-6
104 x
10
=6.76 x 10-11 N m2kg-2

Estimate the mass of the earth , Given radius of the earth r=6.4 x
106 m,acceleration due to gravity g=9.8ms -2 and gravitational constant G= 6.67x
10-11
g = G M/R2
x 106m
g=9.8m/s2
M= g R2
G =6.67 x 10-11
Nm2 kg-2
R = 6.4
9.8 x ( 6.4 x 106 ) 2
6.67 x 10 -11
G
After simplification we get
=
=
Q
V
601 x 1022
6.01 x
1024
=
6 x 1024
kg
Match the following
A
Ans



Force between sun and moon
force
Gravitational constant
Simple pendulum
action at a distance
Nm2 kg -2
used
to determined acceleration
due
to gravity

Newton’s law of gravitation
m2/ d2
F= Gm1
Heat
Q I
Choose the correct answer.
1
Bimetallic strip is made up of
2
Specific heat depends on
3
In a thermostat device which parameter remains approximately constant temperature.
4
Unit of co-efficient of linear expansion
5
Density of water is maximum at
Q II
1
Metals with different linear expansion coefficient.
mass of material.
K -1
4 0C
Fill in the blanks.
Unit of heat capacity is
Joule /Kelvin of Joule /Celsius
2
On heating a rod, its length increases.
3
Unit of latent heat is
4
Expression for latent heat of fusion = L= Q/m
5
The atomic mass of an atom is 23 and its atomic number is 11 , the atom has ----------------
Q III

J /Kg
Answer the following
Mention the effects of heat on a substance
The effects of heat on a substance are change of physical state, thermal expansion and increase
in temperature.

Give two illustrations of thermal expansion from day today life
A
Two illustrations of thermal expansion in day to day life are
i)
During winter electric wire between two poles looks very tight. But during summer it
look loose and hangs due to thermal expansion.

If the lid of a bottle is found very tight, just heat the neck of the bottle a little.
Immediately the lid comes out due to expansion.
3
What is bimetallic strip? Mention any two applications of it.
A
A metallic strip prepared by revetting two dissimilar metals with different expansion
coefficients is called a bimetallic strip. They are used as thermostatic swi tches in electric irons
refrigerator
4
Define heat capacity of a substance. Mention its unit
A
Specific heat of a substance is the quantity of heat required to raise the temperature of unit
mass of it through unit temperature. Unit of specific heat is J /Kg K

Give two illustration of high heat capacity of water
A

Water is used as a coolant in the radiations of cars. It absorbs more heat without much rise
in temperature as it has high specific heat capacity.

Hot water bags are used for fermentation. Water does not cool quickly because it has high
specific capacity.
6
Describe an experiment to demonstration the cubical expansion in solids.
A
For figure refer page no. 40
fig 3.2 a
and
3.2
b
Take a metal ball and a metal ring of suitable radius, such that the ball can just pass through the
ring when both are the same temperature. Then heat the metal ball and try to pass it through
the ring. The ball will not pass through because heating the metal ball increases its diameter and
hence its volume.
7
Define latent heat of vaporization.
A
The amount of heat required to convert unit mass of the liquid at its boiling point
completely into vapour, without rise of temperature is latent heat of vapourisation.
8
Ice at 00C is a better coolant than water at 00C, justify
A Ice at 00C is in solid state hence it absorbs heat from surrounding objects to make it liquid.
But water at 00C contains latent heat in it, hence water does not become a better coolant.
IV solve the following problems

The length of a brass scale is 1m at 280 C. If the coefficient of linear expansion of brass is
18X10-6/0C what is its new length at 680C ?
A
L2 – L1 =L1( T2 – T1 )
T1 = 280C,
L1 = 1m
T2 = 680C
α= 18x10-6/0 C
L2 – 1 = 18 x 10-6 x 1 (68 -28)
L2 – 1 = 18 x 10-6 (40)
L2 – 1 = 720 x10-6
L2 = 0.00072 + 1
L2 = 1.00072m

A body of mass 0.5kg requires 3000 J of heat in order to raise its temperature from 35 0C to 450C.
Calculate its specific heat.
A
S = Q / mΔT
Q = 3000 J,
m = 0.5 kg
T 1 = 350C
T2 = 450C
S = 3000/ 0.5 ( 45 – 35 )

= 3000/0.5X10 = 3000/5 = 600J/kg/ 0 C
A metal rod of length 0.5 m at 200 C becomes 0.5006m at 950C. Find the coefficient of linear
expansion.
A
α = L2 – L1/ L1 ( t2 – t1 ) = 0.5006 – 0.5/ 0.5 ( 95 – 20 )
α = 0.0006/ 0.5 X75 = 0.006/375
= 16X10-6/oC
IV Match the following
A
B
1 Heat
energy
2 bimetallic strip
different linear expansivity
a form of
made of two metals with
3 Density of water
4 Specific heat
maximum at 4 0C
J/kg 0 C
Nature of
Light
Textual Questions and Answers
I Choose the correct answer
1 The packets of energy are called -----Photons
a. Electrons
c. photons
b neutrons
d positrons
2 Corpuscles are the tiny particles of -----light
a. Light
c. Waves
b sound
d radiations
3 Which of the following formula represents of photon ? ---- E= hc/λ
a. E= hc/λ
b E=λ/hc
c. E=h/λc
d E=h/λ
II Fill in the blanks
1. Light has particle and wave nature.
2. Light waves travels in the form electromagnetic waves.
3. Electromagnetic waves are transverse waves.
III Match the following
A
B
1. Corpuscular theory
a) Newton
2. Wave theory
Huygens
3. Electromagnetic theory
4. Quantum theory
planck’s
b)
c) Maxwell’s
d) Max
IV Answer the Following
1. Why was corpuscular theory of light discarded?
A. Newton explained reflection, refraction, and dispersion using
corpuscular theory but failed to explain other characteristics like
diffraction, interference and polarisation. Hence corpuscular theory
failed.
2. Can the wave theory of light explain the phenomenon of photo
electric effect? Justify
A. Wave theory of light cannot explain photo electric effect. But
quantum theory explains photo electric effect.
3. Which theory of light proposed the presence of ether as medium, for
propagation of light?
A. Huygens wave theory of light proposed the presence of ether as
medium of propagation. But this theory was not admitted.
4. Light energy is propagated in the form of particles having wave
nature. Justify this statement using quantum theory of light.
A. According to Max Planck light emission or absorption of energy is not
continuous but takes places in discrete units. These discrete units are
quantum (energy packets). The particles move in wave form with
energy in them.
5. Which theory explains all the characteristics of light?
A. Quantum theory (later known as photon theory) has a greater ability
to explain most of the characteristics of light.
6. What is meant by electromagnetic radiation?
A. Electromagnetic radiation is an electromagnetic field wave. It is
caused due to fluctuating electric field and magnetic fields. These
radiations are transverse waves and travel in vacuum.
7. Name any two characteristics of light explained by Huygens wave
theory.
A. i. According to Huygens light travels in the form of mechanical
waves.
ii. Light travels through a medium known as Ether, an imaginary
medium.
8. You might have seen mercury street lamps. The blue light glow given
by these lamps has wave length of 436 nm. What is its frequency?
A.
/λ
or
C =γλ where C
velocity of light
γ = frequency and λ = wave length
= 436 X 10-9m
γ = 3X10 8 / 436 X 10-9
=
17
= 688X1012Hz
9. Yellow colour seen in fireworks is due to the emission of light with
wave length around 588nm when sodium salts are burnt. Calculate the
frequency of yellow light of wave length 588nm.
A
γ=
or C = γλ
where C = 3 X 10 8m
γ = wavelength 588nm
γ = frequency
γ = 3X 108 / 588 X10-9
= 1017/196
= 51 X 1013Hz
Photoelectric effect
I choose the correct answer
1The electromagnetic radiation that can produce photo-electric effect in all the metals is gamma rays.
2A person wearing a black shirt and white cap is standing in front of a T.V camera. His image is captured
by photocells of T.V camera. The part of the photocells of T.V camera. The part of the photo cell which
captures image of his cap emits more number of photo-electrons. This is related to intensity.
3The property of laser used in laser ranging is non diverging nature.
4Radio waves cannot produce photo-electric effect on the known metal because radio waves have lower
frequency.
5The following cannot be explained by wave nature of light photoelectric effect.
II Fill in the blanks
1 The energy of photon is given by the formula
2
E=h
Light energy can be converted can be converted into electricity by solar panel
3 The minimum frequency of incident radiation to produce photo electric effect is called threshold
frequency.
4The kinetic energy of photo-electrons is directly proportional to the factor frequency.
5Laser light when passed through a glass prism cannot produce band of colours because it is
Monochromatic.
III Give scientific reasons for the following
1 Sodium metal can produce photo electric effect for ordinary visible light.

Threshold frequency of ordinary light is enough for sodium metal to produce photoelectric
effect. Also the intensity of ordinary light is enough to release photoelectrons from sodium
metal.
2. A 40W bulb and 60W bulb though have different intensities cannot change the kinetic energy of the
photoelectrons produced by them from a substance.
A. Even though intensities are different of 40 watt bulb and 60 watt bulb , their frequency will be
the same . Therefore kinetic energy does not change .
3.
Ordinary key chain laser light shouldn’t be directly viewed.
A. Ordinary key chain laser light is mild . But it has high direction with narrow beam. This spoil the
retina of eyes .
4.
Laser is used in cutting metals
A . Laser has high energy density together with non- diverging property makes it suitable for
cutting metals.
5.
Silicon voltaic cells are used in solar electrical energy devices.
A.
Silicon voltaic cells produce electric current with the hel p of solar energy and can be used in
electrical energy devices.
IV Answer the following questions
1The time taken by laser to travel from tower ‘A’ to tower ‘B’ and then to reflect back to tower ‘A’ from
mirror of tower B is 0.0001 seconds. Calculate the distance between the two towers.
A v=d/t
.‘. d= vXt/2
v= 3X108m/s
t = 0.0001 seconds
.’. d = 3 X 108 X 0.0001/2
=3/2 X 108 X 10-4 = 1.5 X 104
d = 1.5 X 104m
2Distinguish between ordinary light and laser light.
A
Laser light
Ordinary light
1 Monochromatic
1
Poly chromatic
2 Highly directional as a narrow beam. 2
Light scatters and
spreads
3 Coherent
3
incoherent
4 High intensity
4 low intensity
3.
What is dual nature of light ?
A.
Light travels in the form of particles known as photons as well as wave form. This is dual
nature of light.
4.
List the application of photoelectric effect.
Ans
i
Applications of photoelectric effect.
In TV cameras photo cells are used to convert visuals light into electrical signals.
ii
In cinematography to produce sound.
iii Used for automatic switching on and off of street light.
iv Used in automatic control of traffic signals.
v Used in counting machines.
vi Used in the operating of burglar alarms.
Vii In solar voltaic cell
5Draw a neat diagram of He-Ne tube.
Refer page no 312
6
Fig
23.11
List any 3 uses of laser.
A 1. Laser is used in industries for cutting and welding metals.
2.
Laser is used in optic fiber communication
3
In three dimentional
7.
known as holograph laser is used.
Suggest any two situation in which photocells can be used as automatic switches.
A i)
Automatic light and fan switch off device, which can be used at home. When a person or
members of the family go out from the room, light and fan switches are automatically put off, so
that electricity can be saved.
ii)
Automatic gate opening and closing device using photocells can be constructed. When the head
light of owner’s car falls on the gate, it will be opened and closed when he enters into the
house. Head light of other car wont create any effect on this
8
What is laser beam holograph?
A Using laser beam obtaining three dimentional images in printed form is known as laser beam
holography.
9
How can photoelectric effect be used to produce electricity?
A When sunlight falls on solar panel containing large number of silicon cells electricity is produced.
Silicon cells absorb sun’s energy and convert it in electric energy.
10What are spontaneous emission and stimulated emission?
A i Spontaneous emission- consider two energy states of an electron, the ground state (E1) and the
excited state (E2). An electron from an orbit of higher energy (E2) transits to an orbit of lower energy (E1)
on its own by emitting a photon of energy E2 – E1 = h where ‘h’ is Plank’s constant and is frequency of
the photon. This is known as spontaneous emission.
ii Stimulated emission – photons of energy equal to the E3 – E1 are excited to E3 because of
absorption of energy. Most of the electrons return to the state of E 1 by spontaneous emission. But some
electrons transit from E3 – E2. These electrons remain for a few milli- seconds ( 3 X 10-3 ). Such an
electronic state is called metastable state. If another photon of same energy is incident on it, the
electron transits to E1 and emits a photon which is exactly the same as the incident photon. This type of
emission is called stimulated emission.
Q 11 What is photoelectric effect? Give Einstein’s explanation of the phenomenon
A
The phenomenon due to which certain metals emit electrons when exposed to light is called
photoelectric effect. The electrons emitted by photoelectric effect are called photo electrons.
Albert Einstein used Plank’s quantum theory according to which all electro magnetic
radiations are discrete energy packets called photons. Whenever light is incident on a system,
either photons are absorbed or photons are emitted or photons pass through. When a photon
of frequency higher than the threshold frequency of a metal collides with an electron of the
metal then the electron gets ejected.
Q 12.
What is population inversion?
A
The process of exciting the atoms( electrons) from lower state to higher energy state is called
population inversion.
Q. 13 Explain an experiment to demonstrate photoelectric effect .
A
For diagram
refer page no
A zinc metal plate was polished to remove the deposit of oxides and dirt. It was
exposed to a source of ultraviolet rays. An electroscope detected that zinc plate gets positively charged
when uv rays are incident on it. When electrons are emitted from zinc plate, it be came positively
charged.
Q .14
State the factors on which the following depend.
i) Kinetic energy of photoelectron,
ii) Number of photoelectron
A
i)Kinetic energy of photoelectron---- when the frequency of the light is more than the
threshold
frequency , kinetic energy of photoelectrons increases.
ii) number of photoelectron---- when intensity of light is more number of photoelectrons
increases.
The Sun


III
Fill up the blanks

Aurora effect can be demonstrated in the science laboratory also by using coloured
glasses and light

The colour of chromosphere is pink.

Solar flares are associated with intense magnetic field.

Sun is called the laboratory to study other stars because Sun is nearer to earth.

The reason for enormous energy output of the sun is formation of helium.

Harmful effect of solar wind on earth is protected by magnetosphere.

Sun spots on the photosphere are due to comparatively cooler regions.
Fill up the blanks

The innermost layer of the sun is called the core.

The zone that provides an efficient means of transporting energy near the core of
the sun is radiation zone.

The solar wind consists of hydrogen nuclei or protons.

The visible surface of the sun is photosphere.

Corona of sun is visible during total solar eclipse.
Answer the following

Distinguish between solar flares and solar prominences.

The sudden but short lived out burst of energy and matter from the surface of the sun is
called solar flares.
The most prominent flares, which rise very high and loop back due to gravity of the sun,
are called solar prominences.

What are sun spots? To which factor are they related?

Sunspots are dark irregular patches or spots on the photosphere. Sunspots are the
manifestation of the intense magnetic field. The magnetic field prevents some energy
from reaching these regions from the interior of the sun, resulting in the decrease of
temperature.

State Kepler’s 3 laws of planetary motion.

1st law The planet move in elliptical orbits, around the sun with sun at one focus of the
eclipse.
2nd law The line joining the planet to the sun sweeps out equal areas in equal intervals of
time as planet travels around the ellipse.
3rd law The square of the orbital period of a planet is proportional to the cube of the
semi major axis of the orbit.
4
Explain the structure of sun with a neat diagram.
A
For diagram refer page no.374
fig
27.7
The innermost part of the sun is core. Surrounding this core there is convection zone.
Surrounding this convection zone there is radiation zone. Outside this zone there is
photosphere containing granulations and spicules ( thread like structure ). Solar flares and
prominence and sunspots are there on photosphere. Next layer of the sun is
chromosphere. After chromosphere the vast corona area contains plasma state of matter.
5
A
6
A
State the effects of solar activities.
The effects of solar activities are sunspots, flares, prominences and solar wind.
Draw the neat diagram of total solar eclipse showing the corona of the sun.
For diagram page no.
369
Fig 27.1
7
State the layer of earth’s atmosphere which protects us from the radiation of the sun
A
The layer of earth’s atmosphere which protect us from the radiations of the sun is
ionosphere ( magnetic field surrounding the earth )
8
A
Name the nuclear fuel present in the sun
Hydrogen is the main nuclear fuel present in the sun. This undergoes nuclear fusion to
release energy.