PHYSICS
Experiment 12.1
VERIFY THE LAWS OF REFRACTION OF LIGHT USING A GLASS
SLAB
THINK
Q.1 Why should the pins be vertical?
Ans. Pins should be vertical so that we can see the image clear and straight.
Q.2 Can you predict whether a ray of light will bend towards or away the normal
Ans. Yes we can predict
(i)
If light ray enters from dense to rare medium then it will bend away from normal.
(ii)
If light ray enters from rare to dense medium then it will bend toward normal.
POST LAB ACTIVITIES:
Q.1 Refractive index of medium 2 with respect to medium 1 is 2.4. what will be the value
of angle x.
Ans.
sin i
n
sin r
sin 40
sin r
sin 40
sin r 
2.4
.2678
sin r 
2.4
 .2678 
r  sin 1 

 2.4 
r  15.5o
so
2.4 
x  90o  r
x  90o  15.5o
Q.2
Ans.
Q.3
x  74.5
A transparent solid with refractive index n=1.65 is immersed in a liquid of exactly
the same refractive index. The solid disappears. Explain this phenomenon.
The solid will disappear Because refractive index is same. So solid will move vertically
without any change in direction and will disappear.
Find the refractive index of the glass slab by applying geometrical construction on
Fig. 12.1.1 without measuring the angle of incidence and angle of refraction.
Ans. Activity
1
Q.4
Ans.
Q.5
How does this experiment prove the validity of first law of refraction?
Activity
A ray travels from water to air at an angle of 40o with the normal. Find the angle of
refraction is the air if the refractive index of water is 1.33.
Ans.
sin r
sin i
sin r
1.33 
sin 40
n
1.33  sin 40  sin r
1.33  0.267  sin r
.3561  sin r
r  sin 1 .3561
Q.6
Ans.
r  21o
When you look at reflection in a sheet of glass, you often see a double image. Why?
a. Due to dispersion of light.
b. Due to poor quality of glass material.
BRAIN TEASER
Q.1 Why does a stick immersed obliquely in water appear to be bent or short? Explain
with the help of a ray diagram.
Ans. This is due to refraction of light from water to air. Our eye cannot observe bending of
light so a stick appears to be bend in water.
Q.2 Why do faces of the person sitting opposite to you around a camp fire appear to
shimmer?
Ans. This is due to reflection of light from the faces of the persons.
Experiment 12.2
FIND THE REFRACTIVE INDEX OF WATER BY USING A CONCAVE
MIRROR
THINK
Q.1 What happens to the image by pouring water on the mirror?
Ans. Because parallax will reappear due to refraction of light from water instead of glass
Q.2
(i)
How will the refractive index be affected using more amount of water?
Ans.
h1
because ‘n’ is inversely proportional to the depth of water h2.
h2
So by placing more water on mirror n will be changed.
As you know that n 
2
(ii)
Explain why the index of refraction of air is smaller than the index of
refraction of a solid.
Ans. Because density of air is less than density of solid, so refractive index of solid is greater
as ‘n’ is the direct measurement of density.
POST LAB ACTIVITIES:
Q.1 On the diagram, draw the path of the ray of light from the coin to her eyes.
Ans.
Q.2
Ans.
Q.3
What happens to light when it passes from water into air?
When light passes from water into air, it will bend away from normal.
The girl sees a virtual image of this coin. Mark ‘x’ on the diagram to show where
this image is formed.
Ans.
BRAIN TEASER
Q.1 A hunter with his fishing spear does not aim his spear at where the fish appears to
be. Explain.
Ans. Because due to refraction of light he sees the image of the fish, so he missed the aim.
Q.2 A swimming pool appears to be shallower than its real depth is, why? Explain with
the help of a ray diagram.
Ans. A swimming pool appears to be shallower than its real depth due to refraction of light in
water.
Q.3 A solid and a liquid have the same refractive index. What happens on dropping the
solid into the liquid?
Ans. When we will drop solid into liquid it will disappear without bending because both have
same refractive index.
Experiment 12.3
3
DETERMINE THE CRITICAL ANGLE OF GLASS USING A SEMICIRCULAR SLAB AND A LIGHT RAY BOX / OR BY PRISM.
THINK:
Q.1 Why should the ray of light be perpendicular to the semi circular edge?
Ans. The ray of light should be perpendicular to the semi circular edge to keep it un-deviated
POST LAB ACTIVITIES:
Q.2 Complete the diagram to show where the fish appears to be.
Ans.
Q.3
Why does a road appear wet when one looks out of a car at a distant point in a
summer afternoon?
Ans. A road appear wet due to total internal reflection of light between hot and cold layers of
air.
Q.4 Can total internal reflection occur when light travels through water to a boundary
with glass?
Ans. Not possible as light should enter from dens to rare medium for total internal reflection.
Extended Activities
Q.1 If a ray box is not available what alternative method can be used to find the critical
angle?
Ans. We can use prism
Q.2 Find the refractive index of glass with the help of the same apparatus by applying
Snell’s Law.
Ans. Activity
Q.3 Obtain a light spectrum using a ray box and a prism.
Ans. Activity
BRAIN TEASER
Q.1 Why a fish deep in water is able to see the fisherman standing at the river bank?
Ans. Due to refraction of light from air to water fish is able to see fisherman standing at the
bank.
Experiment 12.4
4
TRACE THE PATH OF A RAY OF LIGHT THROUGH GLASS
PRISM AND MEASURE THE ANGLE OF DEVIATION.
THINK
Q.1 Does the angle of deviation remain the same for different angles of incidence?
Ans. No it will not remain same as angle of deviation inversely related with angle of incidence.
After a limit angle of deviation is directly related with angle of incidence.
Q.2 What happens if line PQ is not slanting to line AB?
Ans. It will refract un-deviated.
POST LAB ACTIVITIES:
Q.3 You are given a hollow prism. Fill it with water and find the angle of incidence and
corresponding angle of refraction. Determine the refractive index of water.
Ans. Activity
Q.4 A triangular prism is shown in the figure. The angles of prism are 90, 45 and 45.
what can you say about the refractive index of the prism?
Ans. Refractive index is not related with angles of the prism. It is related with the density of
the material of the glass.
Extended Activities
Q.1 Repeat the experiment to take at least six readings. Now plot a graph between angle
of incidence and angle of deviation. Determine the value of angle of minimum
deviation.
Ans. Activity
Q.2
Determine the refractive index of the glass prism by using the formula.
 A D 
sin 

 2 
n
 A
sin  
2
Ans.
Q.3
Ans.
Activity
Construct a periscope by using two right angle prisms.
Activity
Experiment 12.5
FIND THE FOCAL LENGTH OF A CONVEX LENS BY PARALLEX
METHOD.
THINK
Q.1 Why should the object needle be placed at more than one focal length away from the
lens?
Ans. The object needle should be placed at more than one focal length away from the lens, to
get real and inverted image of the object.
POST LAB ACTIVITIES:
5
Q.2
Ans.
Q.3
Ans.
Q.4
Ans.
Q.5
Ans.
Take three more readings in the above experiment and draw a graph between (pq)
along y-axis and (p+q) along x-axis. Find the slope or gradient of the graph. What
does this slope represent?
Activity
How can you make a set of rays coming from a single point to form a parallel beam
of light?
We can make a set of rays coming from a single point to form a parallel beam of light by
placing source of light at principle focus of convex lens.
By measuring approximate focal length of different convex lenses, investigate, how
the focal length of a lens is related to its thickness?
Focal length of a thick lens will be short and of thin lens will be log.
Explain the difference between a real image and virtual image.
(i)
(ii)
Real image can be obtained on screen and virtual cannot.
Real image is inverted and virtual images is erected.
BRAIN TEASER
Q.1 If object needle is replaced by a lighted candle, what arrangement would be needed
to obtain its image?
Ans. If object needle is replaced by a lighted candle, we should place a screen for image of
candle and we should avoid from air interruption.
Q.2 Would you be able to obtain the image of the candle on a screen if it is placed within
the focal length of the lens? Explain with the help of a ray diagram.
Ans. No, because the image will be virtual and will be on the same side of the candle which
cannot be obtained on screen.
Q.3 If half of a convex lens is covered by an opaque object, what shape of image would
be obtained on the screen?
Ans. If half of a convex lens is covered by an opaque object, than image will be of the same
size but a little dim.
Experiment 12.6 (a)
SET UP A MICROSCOPE
THINK
Q.1 Why the objective lens of microscope has short focal length and not a long one?
Ans. Objective lens of microscope has short focal length so that less light disperse and we
obtain the sharp image of the object.
POST LAB ACTIVITIES:
Q.2 Identify a simple microscope in the laboratory. What is another name of this device?
Ans. An other name of simple microscope is magnifying glass.
6
Q.3
Ans.
Q.4
Ans.
Is it possible to make an optical microscope so strong that the atoms that make up
everything would be visible?
No, it is not possible to make an optical microscope so strong that the atoms that make up
everything would be visible
You are provided with a lens of shorter focal length than that you used earlier as an
eyepiece. How the magnification of a given microscope will be changed?
When we use a lens of shorter focal length as eyepiece than magnification will increase
as both are inversely related with each other, but resolution of microscope affect.
BRAIN TEASER
Q.1 What effect in the working of a microscope is observed if plano-convex lenses are
used instead of double convex lenses?
Ans. Light will not converge properly and will affect the sharpness of the image.
Experiment 12.6 (b)
SET UP A TELESCOPE
THINK
Q.1 Why has the eyepiece lens of telescope short focal length and not a long one?
Ans. The eyepiece lens of telescope has short focal length to avoid dispersion of light and to
get final image sharp and clear.
POST LAB ACTIVITIES:
Q.2 Find the length of telescope in the above experiment.
Ans. Length of telescope can be find by the following formula
L= fo + fe
Q.3 Replace the objective with another lens of larger focal length. What will be new
length of the telescope? Compare the lengths of telescope in both the cases?
Ans. By replacing the objective lens of telescope by another lens of large focal length then
length of telescope will increase.
Q.4 Determine the magnifying powers of the telescope in both the cases?
Ans. We can determine magnifying power of telescope by the following formula.
M 
fo
fe
BRAIN TEASERS!
Q.1 What changes are required to reduce the length of a telescope?
Ans. We will reduce focal length of both lenses so that size may reduce and magnification
does not effect.
Q.2 What is the difference between a telescope and a binoculars?
Ans. The differences between a telescope and a binocular are:
(i)
Both have different ranges
(ii)
In telescope we observed by one eye and in binocular with both eyes.
7
(iii)
In binocular totally reflecting prisms are used but in telescope lenses are used.
Experiment 14.1
SET UP A TELESCOPE
THINK:
Q.1 Why should the slider of the rheostat be kept in the middle?
Ans. Slider of the rheostat is kept in the middle so that we may either increase or decrease the
resistance of the circuit.
POST LAB ACTIVITIES:
Q.1 A switch can act both as a conductor and as an insulator. Comment on the
statement.
Ans. When switch is on then it will behave like a conductor and when it is off then will behave
like an insulator.
Q.2 Determine the value of resistance R of the conductor from graph drawn for
nichrome wire.
Ans. We can find resistance of conductor by finding slope of the graph.
Q.3 Connect a 6V bulb in the circuit in place of nichrome wire. Take five reading of V &
I. Draw V versus I graph. Does it verify Ohm’s Law?
Ans. Activity
Q.4 Repeat the above experiment by using nichrome wire of double the length. Draw its
V-I graph on the same graph paper. What do the two different straight lines show
with reference to the slope? Can you tell which of the two wires has greater
resistance?
Ans. Activity
BRAIN TEASER
Q.1
What does this graph indicate?
(i)
From A to B
(ii)
From B to C
(iii) Name the device which follows this graph.
Ans.
(i)
(ii)
(iii)
From A to B graph indicates that V and I are directly proportional to each other.
From B to C graph indicates that V and I are not directly proportional to each
other.
Thermisters follow that type of graph as current increases when resistance will
decrease in then.
Experiment 14.2
SET UP A TELESCOPE
THINK
8
Q.1
An ammeter has a very low resistance. How should it be connected to a circuit
components?
Ans. Ammeter should be connected in series with rheostat and circuit components
Q.2 Voltmeter has a very high resistance. How should it be connected to a bulb?
Ans. Voltmeter should be connected in parallel to the bulb because of its high resistance.
Q.3 Why does the current in the circuit not change when the voltmeter is connected
across any resistor?
Ans. Voltmeter is attached in a circuit parallel, due to its high resistance, no current flows through it.
Therefore current in a circuit will not change by connecting a voltmeter in a circuit.
POST LAB ACTIVITIES:
Q.1 Festive lights used for building decorations are made by connecting many small
bulbs in series. If one of the bulbs gets fused, would the others continue to glow?
Explain the reason.
Ans. No it will break the flow path of current and circuit will break.
Q.2 Select any two suitable resistors of known values and join them in series by using
the apparatus given in experiment No. 14.2.2 to make an electric circuit. Find the
equivalent resistance of the resistors experimentally and then compare it with its
value calculated theatrically.
Ans. Activity
Q.3
A high resistance of 12000 is connected in series with a galvanometer to form a
voltmeter. If the resistance of the voltmeter is 12150, what is the resistance of the
galvanometer?
R e  R1  R2
Ans.
12150  12000  Rg
Rg  150
9
Q.4
Q.1
Ans.
BRAIN TEASER
Six bulbs are connected in series in a circuit. If two more bulbs are added in series
with them, what will be the effect on the brightness of the bulbs now? How will be
the current affected? Give reasons.
Current of circuit will reduce due to increase in resistance and consequently brightness
will also reduce.
Experiment 14.3
STUDY RESISTORS IN A PARALLEL CIRCUIT
POST LAB ACTIVITIES:
Q.1
Ans.
Resistance of values 1, 100 and 1000 are connected in parallel. What is the equivalent
resistance of the combination? What conclusion do you draw from this example?
1
1 1
1
  
Re R1 R2 R3
1 1
1
 

1 100 1000
1000  10  1

1000
1 1011

Re 1000
1000
1011
R e  0.99
Re 
Q.2
An ammeter is formed by shunting a galvanometer with a low resistance. If the
resistance of the galvanometer is 50 ohm and a that of the shunt is 0.0001 ohms,
what is the resistance of the ammeter?
Ans.
1
1
1


Re
R1 R2
1
1
1


Re
50 0.0001
1
 0.02  10000
Re
1
 10000.02
Re
1
10000.02
R e  0.0001 
Re 
10
Q.3
A current of 2mA is passing through a resistance of 1k (Fig. 14.3.2a).
What is the potential difference across it? A voltmeter of 1k is connected across
this resistance to measure the potential difference (Fig 143. 2b). What potential drop
will be indicated by the voltmeter? What conclusion do you draw from this
example?
Ans.
1 1 1
 
Re 1 1
1
 2k 
Re
1
2k 
Re  0.5k 
Re 
Now
V  I Re
V  2mA  0.5k 
Q.4
Ans.
Q.5
Ans.
Q.6
V  1V
Voltage drop will be same
What arrangement, parallel or series, would you use to connect the lights in a room?
Explain your reason.
We will used parallel arrangement, so that same voltage is provided to all the appliances
Why the main fuse wire is connected in series with the electric meter in an
household electric circuit?
Main fuse wire is connected in series with the electric meter in an household electric
circuit so that fuse can stop access flow of current and can prevent damages.
Consider the given circuit. What is the potential difference across the two bulbs and
current passing through each bulb?
Ans.
I1 
V
R1
3
2
I1  1.5 A
I1 
I2 
V
R2
3
2
I 2  1.5 A
I2 
11
EXTENDED ACTIVITY
Q.1 Design an experiment to find the equivalent resistance of three resistors such that
one resistor is connected in series with the parallel combination of other two.
Compare it with theoretically calculated result.
Ans. Activity
BRAIN TEASER
Q.1 What will happen if the electrical appliances are connected in series in a household
electrical circuit?
Ans. If the electrical appliances are connected in series in a household electrical circuit then
voltage will dived among all appliances which will reduce performance of the appliances.
If one appliance got damage then whole circuit will break.
Q.2 What will happen to a circuit if a student by mistake interchanges the positions of
ammeter and voltmeter?
Ans. If a student by mistake interchanges the positions of ammeter and voltmeter then
voltmeter will stop the flow of current in the circuit.
Experiment 14.4
FIND THE RESISTANCE OF GALVANOMETER BY HALF
DEFLECTION METHOD
THINK
Q.1 Why a high resistance is taken out from the resistance box before closing the key
K1?
Ans. A high resistance is taken out from the resistance box before closing the key K1 to control
the amount of current and avoid burning of galvanometer
Q.2 Why does the deflection become zero on closing the key K2
Ans. The deflection become zero on closing the key K2 because an alternate path is provided
to circuit and no current will flow through galvanometer.
POST LAB ACTIVITIES:
Q.3 Determine the resistance of the galvanometer by adjusting shunt resistance so that

the deflection  is reduced to .
3
Ans. As the galvanometer shows one third deflection, so
IG 
1
3
Rs
I
I
3
Rs  Rs
or
3Rs  Rs  RG
or
RG  2 R2
12
Q.4
Resistance of the galvanometer is due to a coil fixed inside it. Why do not we directly
measure its resistance like an ordinary resistor?
Ans. We do not directly measure the resistance of galvanometer due to low resistance of its
coil.
BRAIN TEASER
Q.1 What will happen to the reading of an ordinary galvanometer if a strong magnet is
brought near it?
Ans. When a strong magnet is brought near an ordinary galvanometer then reading will
increase due to rate of change of flux.
Q.2 Can you measure the resistance of a voltmeter by half deflection method?
Ans. We can not measure the resistance of a voltmeter by half deflection method due to high
resistance of voltmeter.
Experiment 15.1
TRACE THE MAGNETIC FIELD DUE TO A BAR MAGNET
THINK
Q.1 Why is the compass needle adjusted along the drawn line?
Ans. Compass needle adjusted along the drawn line, so that we can find the north pole of
earth.
Q.2 Why is it necessary to draw the boundary of the drawing board?
Ans. It is necessary to draw the boundary of the drawing board, so that north pole of the earth
will not dislocate.
POST LAB ACTIVITIES:
Q.1 Place two bar magnets parallel to each other at 8 cm apart with their north poles
pointing in the same direction. Plot the magnetic field lines in the space between the
magnets and outside the magnets. Where is the field stronger?
Ans. Field will be stronger on opposite sides
Q.2
Ans.
Draw the magnetic filed of a U-magnet.
N
Q.3
S
Why does a compass needle align itself up with the magnetic field?
13
Ans.
A compass needle align itself up with the magnetic field due to attraction of opposite
poles of the magnet and compass.
Q.4
Ans.
Give three examples of domestic appliances in which permanent magnets are used.
In the following domestic appliances permanent magnets are used
(i)
Speaker
(ii)
DC Motor
(iii)
Generator
(iv)
Computer
BRAIN TEASER
Q.1 A boy was placing the bar magnet near the fire. Why is it not advisable?
Ans. By placing the bar magnet near the fire, it may demagnetize due to heat.
Q.2 A magnet is surrounded by an iron sheet. How does this sheet protect the
surroundings from magnetic effect?
Ans. Iron sheet will protect the surrounding from magnetic effect, because it will limit the
magnetic field inside the cover.
Q.3 A magnet is cut into two pieces from the middle. Will North and South Pole be
separated?
Ans. Not possible, both parts will have their own north and south poles
Experiment 15.2
TRACE A MAGNETIC FIELD DUE TO CURRENT IN A CIRCULAR
COIL
THINK
Q.1 Why is the magnetic filed line at the center of the coil straight?
Ans. The magnetic filed line at the center of the coil is straight because field is strong and
uniform at the center.
POST LAB ACTIVITIES:
Q.2 Reverse the direction of current and trace the magnetic field again. How does it
differ from the previous one?
Ans. By reversing the direction of current direction of field will also reverse.
Q.3 A loop of wire is in the shape of two concentric semicircles as shown in Fig. 15.2.4.
the inner circle has radius a and the outer circle has radius b. A current I flows
clockwise through the outer net wire and counterclockwise through the inner wire.
What is the direction of the magnetic field at the common center P of the semicircles?
Ans. At point P there will be field free region.
BRAIN TEASER
Q.1 What change in the pattern of magnetic filed will be observed if the shape of coil is
made rectangular rather than circular?
14
Ans.
There will be no change in the pattern of magnetic field because in a close loop field
shape remains same.
Experiment 16.1
SET UP AND STUDY OR, AND, NOT, NOR AND NAND GATES
POST LAB ACTIVITIES:
Q.1 Develop the truth tables for the following circuits.
Ans.
A
B
C
A+B
(A+B).C
0
0
0
0
0
0
0
1
0
0
0
1
0
1
0
0
1
1
1
1
1
0
0
1
0
1
0
1
1
1
1
1
0
1
0
1
1
1
1
1
15
A
B
C
A.B
(A.B)+C
0
0
0
0
0
0
0
1
0
1
0
1
0
0
0
0
1
1
0
1
1
0
0
0
0
1
0
1
0
1
1
1
0
1
1
1
1
1
1
1
BRAIN TEASER
Q.1 Write down a truth table for a three input AND gate. How many possible states does
this system have?
Ans.
A
B
C
0
0
0
0
0
1
0
1
0
0
1
1
1
0
0
1
0
1
1
1
0
1
1
1
This gate will have 8 possible states.
16