SECTION: A EXPERIMENTS

EXPERIMENT NO. 1

METRE BRIDGE- 1

Aim: To determine the resistance the material of the given wire using Meter Bridge.

APPARATUS REQUIRED: Metre Bridge, Galvanometer, plug key, battery, jockey, connecting

wires, Resistance box and the given resistance wire.

Theory

It is based on the principle of a balanced Wheat Stones Bridge. Under balanced conditions

=

Hence, at the balance point of the meter bridge

=

The unknown resistance X =( )

R where R is the known resistance placed in the left gap and

unknown resistance X in the right gap. L cm is the balancing length.

Circuit Diagram:

Procedure

1 Do the connections as shown in the diagram with Resistance box in the left gap and unknown

resistance X in the right gap.

2 Close the key K' and check the circuit by pressing the jockey at the two ends of the bridge

wire to get opposite deflections in the galvanometer.

3 Insert a suitable resistance in the resistance box and find the balancing length ‘l’

4 Repeat the experiment with different values of 'R' in the resistance box.

5 Tabulate the observations and calculate the mean value of "X.

OBSERVATIONS

PRECAUTIONS

1 The connections should be neat, clean and tight.

2 all the plugs in the resistance box should be tight

3 Move the jockey gently over the bridge wire and do not rub it.

4 Null point should be brought between 40cm and 60 cm

5 The plug in the key should be inserted only when the observations are to be taken.

RESULT:

The value of unknown resistance X = --------- ohm

SOURECES OF ERROR

1 The plugs may not be clean

2 The instrument screws may be loose

EXPERIMENT NO: 2

METRE BRIDGE : 2

AIM: To verify the laws of combination ( series ) of resistances sing a meter bridge.

APPARATUS : A meter bridge, A battery, a galvanometer, a resistance box, connecting wires,

two standard resistance coils a plug key and a jockey

Theory

It is based on the principle of a balanced Wheat Stones Bridge. Under balanced conditions

=

Hence, at the balance point of the meter bridge

=

The unknown resistance X =( )

R where R is the known resistance placed in the left gap and

unknown resistance X in the right gap. L cm is the balancing length.

When two resistors ( & )are connected in series , then the combined resistance is = +

CIRCUIT DIAGRAM

Procedure:

1) Do the connections as shown in the diagram with resistance box in the left gap and

resistance in the right gap.

2) Close the key K and check the circuit by pressing the jockey at the two ends of the bridge

wire to get opposite deflections in the galvanometer.

3) Insert suitable resistance in the resistance box and find the balancing length l.

4) Repeat the experiment with different values of 'R' in the resistance box and find .

5) Repeat the above procedure with

6) Then join the above two resisters in series to find

7) Calculate . using the equation X =( )

R

VRIFICATION

Experimental value of ohm

Theoretical value of + = ---- ohm

RESULT:

Within the limits of experimental error, experimental and theoretical values of same.

Hence law of resistance in series is verified.

PRECAUTIONS : ( same as metre bridge 1)

SORECES OF ERROR: ( same as metre bridge 1)

X

EXPERIMENT 3

POTENTIOMETER - 1

AIM :To compare the EMFs of two primary cells using a Potentiometer

Apparatus Required: A potentiometer, Jockey, connecting wires, Battery, Rheostat, Leclanche cell,

Daniel cell, Galvanometer, Rheostat, two way key, way key and connecting wires.

Theory

Basic principle of a potentiometer is " For a wire of uniform crosssection, Potential drop across unit

length of a uniform conductor is a constant i.e. Vi= a Constant

Let and be the EMFs of the two primary celis. and and be their corresponding balancing

lengths then

and

=

CIRCUIT DIAGRAM

PROCEDURE

1) Do the connections as shown in the circuit.

2) Make sure that the positive terminal of the battery and the Primary cells are connected to the same

point A of the potentiometer.

3) Include one of the primary cells (E1) in the circuit with the help of the two way key.

4) Close the key in the primary circuit, and adjust the rheostat so that a suitable current passes through

the circuit.

5) Check the circuit by pressing the jockey at points near terminals A & B. If the deflections in the

galvanometer are in opposite directions the connections are correct.

6) Then find the balancing length for the cell

7) Without changing the position of the rheostat, exclude the cell include the cell E2 in the circuit and

find the corresponding balancing length .

8) Repeat the experiment at different positions of the rheostat.

9) Tabulate the observations

OBSERVATIONS

PRECAUTIONS

1 The connections should be neat and clean

2 The emf of the battery should be greater than the emfs of the primary cells;

3 The jockey should not be rubbed along the wire. It should touch the wire gently.

4 The positive poles of the batter and the cells should be connected to the terminal at the zero

of tne wire.

5 A low resistace rheo stat must be used

SOURES OF ERROR

1 The auxiliary battery may not be fully charged

2 The potentio meter wire may not be uniform cross- section.

RESULT: The ratio of emfs

=

EXPERIMENT NO:4

POTENOMETER II INTARNAL RESISTANCE OF A CELL

AIM: To determine the internal resistance of a primary cell using a potentiometer.

Apparatus Required : Potentiometer, battery, Rheostat, Primary cell, Galvanometer,

resistance box, jockey, plug Keys, connecting wires

Theory: Basic principle of a potentiometer is " For a wire of uniform cross section, Potential

drop across unit length of a uniform conductor is a constant i.e. Vi= a Constant

EMF is the potential difference across the terminals of a source when no current is drawn from

it and the terminal potential difference is the potential difference when a current is drawn

from it.

Let E be the EMF of a primary cell whose internal resistance is to be measured. When th e shunt

resistance S excluded tom the circuit, let" " be the balancing length and hence E α

When the shunt "R" is included, let " be the balancing length and hence V

i.e.

But intemal resistance r=

( )

= (

– 1) R

Circuit Diagram

Procedure:

1) Do the connections as shown in the Circuit.

2) Make sure that the positive terminal of the battery and the primary cell are connected to

the same point A of the potentiometer

3) Close the key alone ( by leaving open) find the balancing length " ".

4) Then close key with a suitable shunt resistance "R", measure the balancing length " "

5) Repeat the experiment with different values of shunt resistance

6) Tabulate the observations and calculate the value of r.

OBSERVATIONS

PRECAUTIONS ( as previous expt)

SOURCES OF ERROR (as previous expt)

RESULT : Internal resistance of the given primary cell = ------- ohm

𝑟 (𝑙

𝑙 – 1) R

R R

ohm Internal

resistance r=

(𝑙

𝑙 – 1) R

Sl no R

ohms

Balancing length

In open circuit

without R (l1 cm )

In closed

circuit

(l2 cm)

Internal

resistance

r =(𝑙

𝑙 – 1) R

EXPERIMENT NO: 5

RESISTANCE OF GALVANOMETER

Aim: To determine the resistance of the galvanometer by half deflection method and to find its figure of

merit.

Apparatus: A Weston type galvanometer, voltmeter, battery, two resistance boxes (one of range

5000ohms and other or range 500 ohms), two onway keys, connecting wires etc.

Theory

The resistance of the galvanometer

where R is the resistance connected in series with the

galvanometer an S is the shunt resistance.

Figure of merit of a galvanometer is defined as the current required for producing a deflection of one

division in the galvanometer.

The figure of merit k=

( ) where E is the emf of the cell and ϴ is the deflection produced with

resistance R Circuit Diagram

CIRCUIT DIAGRAM

Procedure :

1) To find the resistance of the Galvanometer, do the circuit as shown in the fig 1 and see the plugs

of resistance boxes are tight.

2) Take out the plug marked 5000 ohms from resistance box R and insert the key only.

3) Adjust the value of R so that deflection is maximum within the scale.

4) Note the deflection ϴ and R.

5) Then insert the key K2 also without changing the value of R.

6) Find out S so that the deflection in the galvanometer reduces exactly half the value obtained in

the previous Step. Note the value of S.

7) Repeat steps 3 , 4, 5 & 6 for five different values of R and ϴ to get different observations and

adjust S every time.

OBSERVATIONS

PRECAUTIONS

. 1. At the time of making of connections, keys , and , should be removed

2. Insert removed. the key ,, only after taking out a high resistance R

3. All of the connections and the keys should be tight

4. The e.m.f. of the battery should be constant.

SOURCES OF ERROR

1. The e.m.f. of the battery may not be constant.

2. The galvanometer divisions may not be equal.

RESULT

The resistance of the galvanometer G= ohm

Figure of merit of the galvanometer k = amp/div.

K=𝐸

(𝑅 𝐺)𝛳

EXPERIMENT NO: 6

FREQUENCY OF AC MAINS

AIM: To find the frequency of the A.C. mains with a sonometer.

MATERIALS REQUIRED:

Sonometer with non-magnetic metallic wire, horse-shoe magnet, hanger and weights, step

down transformer, paper rider and a meter scale.

Theory: A current carrying conductor, which is placed in a magnetic field, experiences a force.

In case the conductor carries alternating current, the direction of force will be alternately

reversed and the wire will oscillate with a frequency of the A.C.

For a wire of length l and mass per unit length 'm' under a tension T the frequency of vibration

of the wire can be given by- 𝛎 =

√

When an AC is passed through an electromagnet and length l and tension T in the wire is so

adjusted that it is set in to resonant vibration by AC

Frequency of AC = f=

CIRCUIT DIAGRAM

PROCEDURE

1 Set up the apparatus according to the figure shown.

2 Attach a 'weight hanger at the end of the sonometer wire.

3 Stretch the wire with a suitable tension.

4 Arrange the electromagnet over the sonometer wire very close to it as shown.

5 Move the wooden bridges outward to include maximum length of the sonometer wire.

6 Connect the electromagnet to the A.C mains and switch it on.

7 Decrease the length of the wire by moving both the bridges equally inwardly till the wire

vibrate with max amplitude.

8 Measure the length of the wire between the edges of the two bridges and tabulate it in

length decreasing column.

9 Bring the two bridges closer and then adjust the length for maximum amplitude by

increasing it and record it in length increasing column.

10 Repeat the experiment by changing the tension

OBSERVATIONS

PRECAUTIONS

1. The wire should be uniform having no kinks.

2. The horse-shoe magnet should be kept in the middle of the wire between the wedges.

3. The tension should stretch the wire within the elastic limit.

4. Weight of the hanger must also be taken into account.

5. The sonometer wire should be metallic but non-magnetic.

6. The wedges should have sharp edges.

SOURCES OF ERROR

1. The frequency of A.C. mains may not be stable.

2. Knife-edges may not be sharp.

3. Pulley may not be frictionless.

4. The wire may not have uniform area of cross-section.

RESULT:

Frequency of A C supply, f =

= -----------Hz

SECTION : B EXPERIMENTS

EXPERIMENT NO. 7

FOCAL LENGTH OF CONVEX LENS

AIM : To find the focal length of a convex lens by plotting a graph between u and v

MATERIALS REQUIRED: An optical bench, three uprights, a convex lens, a lens-holder, two

optical needles and a half meter scale.

THEORY The focal length f' of a convex lens is related to the object distance 'u' and image distance 'v' by

the formula

+

. In accordance with the sign conventions used, the object distance is

taken to be negative while the image distance is taken negative.

RAY DIAGRAM

PROCEDURE

1) Obtain a clear image of a distant object (suppose a tree) on a screen or on a wall. Measure the

distance between the lens and the wall and record it as rough focal length of the lens.

2) Keep the lens upright near the middle of optical bench and the two needle uprights on either side of

the lens.

3) Adjust the leveling screws which are provided in the optical bench for making the lens vertical. Make

sure that the principal axis of the lens is parallel to the optical bench scale.

4) Place the object pin at a distance of nearly 1.5 times the rough focal length.

5) Now adjust the height of the needle as that of the optical center of the lens.

6) Look from the other side of the lens along its principal axis and locate the real and inverted image

formed with the help of the image needle.

7) Adjust the position of the image needle such that tip to tip parallax is removed between the

image and the image needle

8) Note the positions of object needle and image needle and measure the distances corresponding

from the center of the lens ( U and V respectively ).

9) Repeat the experiment with different positions of the object needle.

10) Tabulate the observations.

11) Plot a U-V graph by taking suitable scale and calculate the focal length.

OBSERVATIONS

PRECAUTIONS

1 Tips of the object and image needles should lie at the same height as the centre of the lens.

2 Parallax should be removed from tip to tip by keeping eye at a distance at least 30 cm away

from the needle.

3 The object needle should be formed at such a distance that only real, inverted image of it is

formed.

SORCES OF ERROR

1 The uprights may not be vertical

2 Parallax removed may not be perfect.

RESULT: Focal length of the given convex lens = ------ cm

EXPERIMENT NO. 8

CONCAVE MIRROR

Aim: To determine the focal length of a concave mirror by finding v for different values o f u

Apparatus A concave mirror, optic bench, meter scale, two optic needles, two uprights and a

mirror holder.

Working formula The focal length of a concave mirror is related to the object distance u and

image distance v by the formula

=

+

Procedure

1 Place the mirror upright near the zero end of the optical bench and two other uprights which

have lateral movement. Make sure that the needles face the mirror.

2 Note down the position of the mirror upright.

3 Place the object needle at a position so that its tip and the pole of the mirror remain on the

same horizontal plane and are separated by a distance1.5 times the focal length of the mirror.

Note down the position of the needle. Locate a clear image of the pin. The image will appear to

be inverted.

4 Place the image needle more than double the focal length of the mirror and adjust its position

so that its tip coincides with the tip off the object needle without any parallax. Note the

position of the needle

5 Change the position of the object needle by 1 cm away from the mirror and readjust the

image needle for removing the parallax.

6 Record at least 5 observations.

OBSERVATIONS

PRECAUTIONS

1 The heights of the tips of the needles and the pole of the mirror should be the same.

2 The parallax should be removed from tip to tip beween the needle and the image of the

object needle.

3 The eye should be kept at least 30cm from the image needle.

SOURES OF ERROR

1 The uprights may not be vertical

2 Parallax removed may not be perfect.

RESULT

Focal length of the given concave mirror = ----- cm

EXPERIMENT NO. 9

GLASS PRISM

AIM: To determine the angle of minimum deviation for a given prism by plotting a graph between the

angle of incidence and the angle of deviation.

MATERIALS REQUIRED: Drawing board, glass prism, pins, drawing pins, protractor, metre-scale, a sheet

of white paper and pencil.

THEORY: The path of light ray through a glass prism is as shown in Fig. The ray bends due to refraction

towards the base of the prism through an angle , called the angle of deviation. For a prism with large

angle, depends upon i and varies as shown in the graph given below. For small values of angle of

incidence i, is large. As i increases, first decreases to (the angle of minimum deviation) and after

that it again increases.

RAY DIAGRAM

PROCEDURE:

1. Fix a of sheet of white paper on a drawing board first and then draw a line XX parallel to the length of

the paper slightly above half of the paper.

2. Now keep the prism ABC on the paper in such a way that the side AB coincides with XY as shown here.

Draw the boundary of prism by using a sharp pencil.

3. Fix two pins M1 and Q1 vertically on the line P which makes angle 300 with the normal The

distance between the pins should be about 8 to 10 cm.

4. Now see the images of pins M1 and Q1 through the face AC of the prism. Fix pins R1 and S1 on the

paper in such a manner that these pins appear to be in the same line as the image of pins M1 and Q1

5. Now take out the pins M1 Q1 and R1, S1 and encircle the pin pricks and mark them as R1 and S1

respectively.

6 Remove the prism. Join R1 and S1 and extend the line so as to meet extended line T1P1. The line joining

R1 S1 is the emergent ray.

7. Note the angle of deviation , i.e., angle E1 F1 S1.

8. Repeat these steps for different values of angle of incidence and determine the corresponding angle

of deviation. Draw separate diagram for each angle of incidence ranging from 30°, 35°, 40°, 45°, 50°, 55°

and 60°.

.9. Plot a graph by taking angle of incidence along the X-axis and angle of deviation along the Y-axis.

PRECAUTIONS

1 The angle if incidence should lie between 300- 600

2 The pins should be fixed vertical

3 The distance between two pins shoud not be less than 10 cm.

4 The same angle of prism should be used for all the observations.

SOURCES OF ERROR

1 Pin pricks may be thick

2 Measurement angles may be wrong

RESULT

1 The i-d graph indicates that as the angle of incidence increases, the angle of deviation first

decreas, attains a minimum value and then again increases.

2 Angle of minimum deviation =

EXPERIMENT NO. 10

REFRACTIVE INDEX OF A GLASS SLAB

AIM To determine the refractive index of a glass slab using a travellingmicroscope.

MATERIALS N REQUIRED Glass slab, travelling microscope, fine saw-dust or chalk powder, a marker.

THEORY Due to the refraction, a point P when seen through a glass slab or any other refracting medium

appears to be raised to P. The apparent depth of slab (= NP1) is less than the real depth (NP). The

refractive index of the material of glass slab is given by

PROCEDURE

1. Keep a travelling microscope at a well-lit place and level it by adjusting the levelling screws.

2. Find the least constant or vernier constant of the vertical scale of microscope.

3. Adjust the position of the eye piece to get the cross wires clearly visible.

4. Make a dark ink mark at P on the base of microscope and focus the microscope on the mark (P). Note

the reading (R1) of the vertical scale.

5. Keep the glass slab on the ink mark and readjust the travelling microscope in order to focus the ink

mark at P1 again. Note down the reading (R2) on the vertical scale.

6. Now sprinkle chalk powder or saw-dust particles on the surface of the glass slab at S. Focus the

microscope on the particles and note the reading R3 of the vertical scale again.

7 Repeat these steps making the ink mark at different positions

8 Record the observations.

OBSERVATIONS

Value of 1 main scale division =

No. of divisions on the vernier scale =

Least count =

=

PRECAUTIONS

1. The microscope should be moved only in one direction to avoid back lash error

2. The particles of chalk powder used should be pretty fine.

SORCES OF ERROR

Themicroscope scale may not be properly calibrated.

RESULT: Refractive index of material of glass slab =

EXPERIMENT NO. 11

REFRACTIVE INDEX OF WATER – LIQUID LENS.

Aim; T find the refractive index of water using a convex lens

Apparatus: Convex lens, a plane mirror, an optical needle, a dropper half meter scale and a stand

FORMULA USED The refractive index of a liquid using a convex lens and a plane mirror is n=2-

PROCEDURE

1. Place the plane mirror upon the horizontal and flat base of vertical stand. Place a convex lens on

the reflecting surface of the plane mirror.

2. Clamp on object needle in vertical rod of the iron stand so that its tip is vertically above the

optical center of the convex lens L.

3. Keeping the eye at least at a distance of distinct vision of the object needle till parallax between

object needle and its inverted image is removed tip to tip. Note the distance a between object

needle and the upper surface of the convex lens b, the distance between the object needle and

the upper surface of the plane mirror using plumb line and half meter scale.

4. Now with the help of dropper put a few drops of the experimental liquid that is water on the

plane mirror. See that no air bubbles are introduced in water in this process.

5. Again adjust the position of the object needle by raising it in upward direction .Hence, find the

new position of the object needle and its inverted image is removed tip to tip.

6. Measure the distance between object needle and the surface of plane mirror using plumb line

and meter scale.

7. Repeat the experiment three more times.

8. Record the observations

PRECAUTIONS

1 Before starting the experiment clean the plane mirror and the lens

2 Clamp the object needle horizontally so that its tip is normal to the principle axis.

3 Parallax should be removed tip to tip

4 Take a very small quantity of water

SOURCES OF ERROR

1 The parallax may not be removed tip to tip.

2 The distances may not be measured correctly.

RESULT:

Refractive index of water =

EXPERIMENT NO. 12

ZENER DIODE

AIM: To draw the I- V characteristics of a diode and to determine its revere break down voltage.

MATERIALS REQUIRED: Zener diode characteristics apparatus and a source of voltage.

Theory

Zener diodes are specially designed diodes which can operate safely when it is reverse biased. The

reverse biasing voltage at which current through the diode increases rapidly is known as zener voltage

or reverse break down voltage.

Procedure

1 Make the connections a shown in to figure.

2 Adjust the position of the potential divider so that the ammeter and the voltmeter read zero.

3 Move the potential divider slowly so that voltmeter reading increases stepwise.

4 At every 0.1 V increase, note the corresponding micro-ammeter readings

5 Plot a graph between voltage along the x-axis and current along y-axis.

6 Find out the break down voltage from the graph,

OBSERVATIONS

PRECAUTIONS

1 The voltage should be increased gradually

2 The micro- ammeter should be connected in series and voltmater in parallel.

SOURCES OF ERROR

The zener diode provided may be faulty.

Result

The reverse break down voltage of the given zener diode =------ volt.