Physics Investigatory Project

(1)

Measuring Earth’s

magnetic field

using Tangent

Galvanometer

Made by: Ankita Tripathi

Roll no: 5648057

(2)

CERTIFICATE

_____________________________________________________________________________________________________________________________________ ____________________________________________________________________________________________________________________________________

This is to certify that Ankita Tripathi of class

XII-B has completed the physics project

entitled: ‘Measuring Earth’s magnetic field

using a tangent galvanometer’, herself and

under the guidance of Mr. Siby Sebastian.

All the work related to the thesis had been

done by the candidate herself. The

approach was sincere and scientific.

Mr. Siby Sebastian Examiner

(Subject teacher)

(3)

ACKNOWLEDGEMENT

I am grateful to the Almighty to give me

strength to successfully complete my

project.

This project wouldn’t have been feasible

without the proper and rigorous guidance

of my Physics teacher Mr. Siby

Sebastian, who guided me throughout

this project in every possible way.

I am deeply indebted to my school for

providing the best of facilities and

environment to bring out our innovation

and spirit of inquiry through this venture.

(4)

Index



Materials Required



Principle



Diagram



Theory



Procedure



Observations



Calculations



Result



Precautions



Sources of error



Bobliography

(5)

Materials Required



_{Tangent galvanometer (TG),}



_{Rheostat (R),}



_{Battery (E),}



_{Ammeter (A),}



_{Key (k)}



_{Reversing key}



_{Connecting wires}



_{Metre scale}

(6)

Principle

When a bar magnet is suspended in two

Magnetic fields B and B

h

, it comes to rest

making an angle θ with the direction of

B

h

.

(7)

Diagram

(8)

(9)

Theory

Tangent galvanometer is an early

measuring instrument for small electric

currents. It consists of a coil of insulated

copper wire wound on a circular

non-magnetic frame. Its working is based on

the principle of the tangent law of

magnetism. When a current is passed

through the circular coil, a magnetic field

(B) is produced at the center of the coil in

a direction perpendicular to the plane of

the coil. The TG is arranged in such a way

(10)

that the horizontal component of earth’s

magnetic field (B

h

) is in the direction of

the plane of the coil. The magnetic needle

is then under the action of two mutually

perpendicular fields. If θ is the deflection

of the needle, then according to tangent

law,

Let I is the current passing through the

coil of radius a with n turns, then the field

generated by the current carrying circular

coil is,

(11)

Equating (1) and (2), we get,

The left hand side of equation (4) is a

constant and is called the reduction factor

(K) of the given tangent galvanometer.

(12)

Now from equation (3) & (5), the

horizontal intensity of earth’s magnetic

field Bh is,

(13)

Procedure

For performing in real life

Connections are made as shown in the figure,

where K is the key, E the battery, A the ammeter, R the rheostat, C the commutator, and T.G the tangent galvanometer.

The commutator can reverse the current through the T.G coil without changing the current in the rest of the circuit.

Taking the average of the resulting two readings for deflection averages out, any small error in positioning the TG coil relative to the earth’s magnetic field Bh .

(14)

The magnetic field can be calculated as

follows:

1. Make the circuit connections in accordance

with the circuit diagram.

2. Using a spirit level, level the base and

compass needle in compass box of tangent galvanometer by adjusting the leveling

screw.

3. Now rotate the coil of the galvanometer

about its vertical axis, till the magnetic

needle, its image in the plane of the mirror fixed at the base of the compass box and the coil ie all these three lie in the same vertical plane. In this setting, the ends of aluminum pointer should reads zero-zero. If this is not so, rotate the box without disturbing the position of the coil till at least one of the

(15)

4. By closing the key K, the current flows in the

galvanometer. Read the both ends of the pointer. Now reverse the direction of current by using the reserve key. when the mean values of deflections shown by the pointer in two cases (i.e. before and after reversing the

current) differ by more than 1o, then turn

slightly the vertical coil until the two values agree. This will set the plane of the coil

exactly in the magnetic meridian.

5. By adjusting the rheostat, bring the

deflection in galvanometer around 45

degree. The deflection should not be outside the range(30-60).

6. Record the reading of the ammeter and the

deflection of the compass needle in a box shown by two ends of pointer of the scale.

7. Reverse the current in the coil of the

galvanometer and again record the current and deflection of needle.

(16)

8. By changing the value of current, take four

Observations

Range of ammeter r=_____________A Least count of ammeter = __________A Zero error in ammeter = __________A Number of turns used (N) = __________ Table for Variation of  with I.

S. No. Value of deflection,  Mean  Tan Ammeter Reading (A) For direct current For reverse current 1 2 3 4 Observed Corrected 1. 2. 3. 4. 5.

Table for radius of tangent galvanometer S. no. Inner diameter d1 Outer diameter d2 Mean Diameter d Mean Radius 1. 2. 3.