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# Horizontal Component of EarthŌĆÖs Magnetic Field Using Tangent Galvanometer

To determine the horizontal component of the EarthŌĆÖs magnetic field using tangent galvanometer.

HORIZONTAL COMPONENT OF EARTHŌĆÖS MAGNETIC FIELD USING TANGENT GALVANOMETER

## AIM

To determine the horizontal component of the EarthŌĆÖs magnetic field using tangent galvanometer.

## APPARATUS REQUIRED

Tangent galvanometer (TG), commutator, battery, rheostat, ammeter, key and connecting wires.

## FORMULA where,

BH ŌåÆ Horizontal component of the EarthŌĆÖs magnetic field (T)

┬Ą0 ŌåÆ Permeability of free space (4ŽĆ ├Ś 10ŌłÆ7 H mŌłÆ1)

n ŌåÆ Number of turns of TG in the circuit (No unit)

k ŌåÆ Reduction factor of TG (A)

r ŌåÆ Radius of the coil (m)

## CIRCUIT DIAGRAM ## PROCEDURE

┬Ę        The preliminary adjustments are carried out as follows.

a. The leveling screws at the base of TG are adjusted so that the circular turn table is horizontal and the plane of the circular coil is vertical.

b. The circular coil is rotated so that its plane is in the magnetic meridian i.e., along the north-south direction.

c. The compass box alone is rotated till the aluminium pointer reads 0┬░ ŌłÆ 0┬░.

┬Ę        The connections are made as shown in Figure (c).

┬Ę        The number of turns n is selected and the circuit is switched on.

┬Ę        The range of current through TG is chosen in such a way that the deflection of the aluminium pointer lies between 30┬░ ŌłÆ 60┬░.

┬Ę        A suitable current is allowed to pass through the circuit, the deflections ╬Ė1 and ╬Ė2 are noted from two ends of the aluminium pointer.

┬Ę        Now the direction of current is reversed using commutator C, the deflections ╬Ė3 and ╬Ė4 in the opposite direction are noted.

┬Ę        The mean value ╬Ė of ╬Ė1, ╬Ė2, ╬Ė3 and ╬Ė4 is calculated and tabulated.

┬Ę        The reduction factor k is calculated for each case and it is found that k is a constant.

┬Ę        The experiment is repeated for various values of current and the readings are noted and tabulated.

┬Ę        The radius of the circular coil is found by measuring the circumference of the coil using a thread around the coil.

┬Ę        From the values of r, n and k, the horizontal component of EarthŌĆÖs magnetic field is determined.

### Commutator:

It is a kind of switch employed in electrical circuits, electric motors and electric generators. It is used to reverse the direction of current in the circuit. ## OBSERVATION

Number of turns of the coil n =

Circumference of the coil (2ŽĆr) =

Radius of the coil r = ## CALCULATION ## RESULT

The horizontal component of EarthŌĆÖs magnetic field is found to be ________

### Note:

i) The magnetic materials and magnets present in the vicinity of TG should be removed.

ii) The readings from the ends of the aluminium pointer should be taken without parallax error.

iii) The deflections of TG is restricted between 30┬░ and 60┬░. It is because, the TG is most sensi tive for deflection around 45┬░ and is least sensitive around 0┬░ and 90┬░. We know that

I = k tan ╬Ė

or dI =k sec2 ╬Ė d╬Ė

d╬Ė/ dI = sin2╬Ė / 2I

For given current, sensitivity d╬Ė / dI maximum for sin 2╬Ė = 1 or ╬Ė = 45┬░

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12th Physics : Practical : Horizontal Component of EarthŌĆÖs Magnetic Field Using Tangent Galvanometer | Physics Practical Experiment