Activity 1

Aim
To assemble the components of a given electrical circuit.
Apparatus and materialApparatus:
A voltmeter and an ammeter of appropriate range, a battery eliminator, a rheostat, one way key.
Material:
An unknown resistance or resistance coil, connectingwires, a piece of sand paper.
Diagram

Procedure
1.Connect the components (Resistors, inductors etc.) in series with each other as shown in diagram and then in
series withthe battery.
2.Connect the ammeter in series with the circuit, to measure the current.
3.Connect the voltmeter in parallel to the resistor, to measure the potential difference.
4.Connect the switch in series with the battery.
5.Assembly of the electrical components in electric circuit is complete.
Utility
It is used for measuring an unknown resistance
RESULT
The components of the electrical circuit were assembled.
PRECAUTIONS
1. The positive terminal of the battery should be connected to the positive terminal of ammeter and positive
terminal of the voltmeter.
2. The ammeter should be connected in series with the resistor and the voltmeter should be connected in parallel
with the resistor.
3. Sand paper should be used to clean the ends of connecting wires and leads of the component terminals.
Grease/oil or oxide layer on their surfaces is insulating in nature and needs to be removed. However, do not clean
the plugs and keys with sand paper. Excessive use of sand paper in such a case will make the plug unfit to be used
with the key.

Activity 2
AIM :
To draw the diagram of given open circuit comprising at least a battery, resistor/rheostat, key, ammeter and
voltmeter. Mark the components that are not connected in proper order and correct the circuit and also the circuit
diagram.

APPARATUS AND MATERIAL REQUIRED :

A given open circuit comprising atleast a cell or a battery eliminator, plug key, resistor, rheostat, ammeter,
voltmeter, connecting wires and sand paper.
PRINCIPLE:
An electrical circuit is functional only if all the components of the circuit are connected in proper order, assuming
that all circuit components/devices are in working condition and key is closed. An open circuit means a break in
some part of a circuit which could be deliberate such as a key in open position or a fault such as broken wire or burnt
out component(s) or loose connection. Some of such circuits are given in Figs.

PROCEDURE
1. Draw the circuit diagrams in your notebook as given by your teacher [Fig. A 2.1(a), (b), (c) and (d)].
2. Consider one circuit and mark in Table A 2.1, the various components which have not been connected in proper
order.
3. Draw the correct circuit diagram.
4. Connect the electrical components according to corrected circuit diagram.
5. Close the key in the circuit to verify if the corrected circuit is functional.

OBSERVATIONS:

RESULT: The electrical circuit assembled as per the corrected circuit diagram is functional.

PRECAUTIONS
1. Ends of the connecting wires should be cleaned with sand paper before making connections.
2. The positive terminal of the battery should be connected to the positive terminal of the voltmeter and positive
terminal of the ammeter.
3. The ammeter should be connected in series with the resistor and the voltmeter should be connected in parallel
with it.
Activity 3
AIM
To study the variation in potential drop with length of a wire for a steady current.
APPARATUS AND MATERIAL REQUIRED:
Potentiometer, battery eliminator of constant voltage, dc power supply or lead accumulator, voltmeter and
ammeter of suitable range, plug key, jockey, rheostat, connecting wires, etc.
PRINCIPLE:
If a steady current is flowing through a wire of uniform area of cross section and having its resistance per unit length
constant, potential drop V across two points of the wire is directly proportional to the length l between those two
points. Mathematically,

Diagram

PROCEDURE:
1. Set up the electrical circuit as shown in Fig. A 6.1.
2. Connect positive terminal of the battery to point A (zero length) of the potentiometer.
3. Connect negative end of the battery to the other end B (point) of the potentiometer wire through an ammeter,
plug key and a rheostat. The ammeter should be connected in such a way that its negative terminal is connected to
the negative terminal of the battery.
4. Connect positive end of the voltmeter to point A and other end to a jockey J.
5. Now close the key K and press the jockey at point B. Adjust the rheostat to get full scale deflection in voltmeter.
6. When jockey is pressed at point A, you will get zero deflection in the voltmeter.
7. Now press the jockey at 40 cm and note the corresponding voltmeter reading.
8. Repeat your observation by pressing the jockey at various lengths like 80 cm, 120 cm etc. which may extend upto,
say 400 cm of potentiometer wire. Record voltmeter reading in each case as shown in Table A 6.1.

OBSERVATIONS
Range of the voltmeter = 0-3 V
Least count of the voltmeter = 0.05V
CALCULATIONS
0.004+0.006+0.005+0.006
K= 4
= 0.00525 v/cm
It is the potential gradient of the wire. Its value is almost constant.

PLOTTING GRAPH :

Plot a graph of V versus I, with V on y-axis and I on x-axis. Slope of the line gives k=0.005 V/cm

RESULT:
The ratio φ = V/l is found to be constant within the limits of experimental error. Its mean value is k=0.00525 V/cm.
The graph shows a linear relationship between V and l .
The value of φ = V/l from the graph is 0.005 V cm–1 .

PRECAUTIONS:
1. Zero error in the voltmeter and ammeter (if there is any) should be corrected by adjusting the screw provided at
the base of the needle.
2. The current in the wire should remain constant throughout the experiment. To ensure this, current should be
drawn intermittently for short duration of time. It should be monitored by an ammeter and readjusted whenever
necessary, with the help of a rheostat.
3. Do not press the wire too hard with the jockey while noting down the observations or else there is a possibility
that the wire will become non-uniform (diameter will change) at these points during the course of time.
4. Check for uniformity of wire at its various points before the start of the experiment. If wire is non-uniform, the
potential gradient will not be constant.

SOURCES OF ERROR :
1. The wire must have a uniform cross section along its entire length. This should be checked by measuring its
diameter at various points before the start of the experiment.
2. Voltmeter may not give accurate reading.

Activity 4
AIM:
To study the nature and size of the image formed by a convex lens on a screen by using a candle and a screen (for
different distances of the candle from the lens).
APPARATUS AND MATERIAL REQUIRED:
A candle, match box, a small candle-stand, a convex lens of small focal length and known thickness, a screen with a
stand, metre scale.
PRINCIPLE:
The position, nature and size of the image of an object formed by a thin convex lens varies with the change in the
position of the object as illustrated in Fig. for some specific positions. It is assumed that both the spherical surfaces
of the lens have same radi of curvature.
Ray Diagrams

PROCEDURE:
1. Fix a thin convex lens on a lens holder and place the screen on the other side of the lens.
2. Focus a sharp, clear and inverted image of the distant object on the screen. This is the rough focal length,
measure it with the help of a metre scale.
3. Mark the position of lens on optical bench or on a table. Fix the lens at this point, label it as ‘O’.
4. Mark a point ‘F’ at both the sides of the lens as focus of the lens by knowing the focal length as calculated in
first step.
5. Mark a point 2F at both the sides of the lens, the distance of 2F from the lens is double the focal length of
the lens.
6. Place a candle on the table or needle on optical bench at distance beyond 2F and adjust the height of the
centre of lens nearly equal to the height of the flame of the candle.
7. To locate a sharp image of the candle flame in the convex lens from the other side of the lens, adjust the
position of the screen and record your observations.
8. Now, place the object, e., the lighted candle or the needle at 2F and record your observations.
9. Now, shift the object between F and 2F and record the observations.
10. Now, place the object at F and record the observations.
11. Place the object between O and F of the lens and record your observations.
12. Draw ray diagrams for all the positions of the object.
OBSERVATIONS:
1. Rough focal length of the convex lens = 12cm

RESULT

PRECAUTIONS
1. This experiment should be performed at a shaded place where no direct light reaches (preferably in a dark room)
otherwise the images may not be distinctly visible.
2. While estimating the rough value of focal length f of the lens by focusing the Sun, do not look at the image directly
as it may hurt your eyes.
3. The uprights supporting the optical elements should be rigid and mounted vertically.

Activity 5
AIM:
To obtain a lens combination with specified focal length by using two lenses from a given set of lenses.
APPARATUS AND MATERIAL REQUIRED
A set of convex lenses of known powers, optical bench with uprights and screen, a source of light providing a parallel
beam of light (a collimator).
Ray Diagram:
PRINCIPLE
A parallel beam of light parallel to principal axis after refraction through a lens either focus at a point or appears to
diverge from a point on the principal axis called the focus point. The distance from the optical centre to the focal
point is called the focal length.
Power of lens The ability of a lens to converge or diverge the rays passing through it is called the power of the lens

Its SI unit is Dioptre. Power of a convex lens is taken as positive. Two or more lenses, placed in contact together to
have a common principal axis, form a lens combination. If f 1 , f2 , ... f n be the focal length of individual lens and F be
the focal length of the combination, then

where P is the power of the lens combination and P1 , P2 , ... Pn are the powers of the individual lenses.
PROCEDURE
1. Calculate the power of the combination of two lenses corresponding to the required focal length.
2. Select a lens from the given set of lenses whose power is smaller than that of the combination of lenses to be
prepared, (if only convex lenses are provided).
3. Calculate the power of unknown convex lens to be kept in contact with the lens of known focal length to obtain a
combination of lenses of desired focal length. Select the lens whose power is close to the calculated power from the
given set of lenses.
4. Set up the optical bench on a horizontal table. Adjust the collimator to direct parallel beam of light along the
optical bench. In case collimator is not available, a plane mirror may be used to direct sunlight along the optical
bench [Fig. A 14.1 (b)] and illuminate a slit with it.
5. Place the two lenses on the uprights such that they are in contact with each other. An upright that can hold two
lenses in contact may also be used or the same may be improvised by fixing the lenses on grooves carved on a
thermocole sheet.
6. Direct a parallel beam of light on the combination of lenses and obtain a sharply focussed image of the source of
light on a screen placed on the other side of the lenses. This can be done by adjusting the distance between the
combination of lenses and screen.
7. Measure the distance of the screen from both the lenses and record it in a table.
8. Repeat the activity atleast three times by changing the position of the lens combination on the optical bench.
Record your observations in each case.
OBSERVATIONS
Focal length of lens L1= 11cm
Focal length of lens L2= 15cm
Focal length of combination F (practically) = 7cm
Focal length of combination F (Theoretical) = 6.34cm
RESULT:
Measured value of focal length of lens combination =7cm
Difference between measured value of focal length and the calculated focal length =0.65cm
The difference between the two could be due to experimental error
SOURCES OF ERROR
1. Thickness of the lenses may cause an error.
2. The peripheral region of the lenses are not in contact.
3. Spherical aberration of the lenses may cause an error in locating the position of the sharp image, i.e., the exact
focal length.
Activity 6