Tangent Galvanometer Viva Questions

Tangent Galvanometer Experiment Viva Questions

(i) What is the tangent law used in Tangent Galvanometer?

(ii) Why do you use long pointer to measure the deflection of the magnetic needle in the compass box?

(iii) Why do we keep a plane mirror below the pointer?

(iv) Is the TG a sensitive instrument to measure current?

(v) The TG requires initial adjustments why?
(vi) When you do the experiments with Tangent Galvanometer, you have to keep all magnetic materials away from it. Explain why?

(vii) What are the disadvantages of Tangent Galvanometer?

(viii) What is meant by the reduction factor of a Tangent Galvanometer?

(ix) The deflections in TG should be between 30° and 60°. Explain why?

(x) Aim of Tangent Galvanometer Experiment

Ans: To determine the reduction factor of a tangent galvanometer and hence to calculate the horizontal intensity at the place.

(xi) Apparatus of Tangent Galvanometer Experiment

Ans: A tangent galvanometer (T.G), accumulator, rheostat, commutator, ammeter etc.
T.G. consists of a circular coil of insulated copper wire mounted vertically on a horizontal base provided with three levelling screws. A graduated compass box is mounted horizontally at the centre of the coil. It is graduated into four quadrant from 0° to 90°. Coils of different number of turns can be used by making connections to the appropriate terminals on the base.

(xii) Theory of Tangent Galvanometer Experiment

Ans: If B, the magnetic field at the centre of a circular coil of radius r and number of turns n carrying a current i is perpendicular to Bh, the earth horizontal intensity at the place, then according to the tangent law, B = Bh tan θ; where θ is the mean deflection in the TG.

Therefore, μo/4π x 2πni/r = Bhtan θ

i.e., 10-7 x 2πni/r = Bhtan θ
i = (107 x Bhr/2πn) x tan θ ;  i = K tan θ ; where K is called the reduction factor of TG.

Therefore, K = i/tan θ

But K = (107 x Bhr)/2πn

Therefore, Bh = (2πnK/r) x 10-7

(xiii) Procedure of Tangent Galvanometer Experiment


Preliminary adjustments

(a) The leveling screws are adjusted till the plane of the coil is vertical. (b) The plane of the coil is brought in the magnetic meridian by making its plane parallel to the magnetic needle in the compass box. (c) Without disturbing the coil, the compass box alone is rotated to make the pointer to read 0 - 0.

To find the reduction factor K of TG

A lead accumulator, rheostat, ammeter and the T.G. are connected in series. The T.G. is connected through a commutator. The commutator is put in one direction and the rheostat is adjusted to get a convenient reading (between 30° and 60°) in T.G. The ammeter reading i is noted. The readings θ1 and θ2 at both ends of the pointer are noted. The current is reversed with the help of the commutator. Again the readings θ3 and θ4 of the pointer are taken. The average of the four readings gives θ, the deflection of T.G. The reduction factor K of the T.G is calculated from the equation.

K = i/tan θ

The experiment is repeated for different values of i by adjusting the rheostat. The average value of K is calculated.

To calculate the horizontal intensity Bh at the place

The radius r of the coil is determined by measuring its circumference.

r = Circumference/ 2π

The number of turns n of the coil is noted. The horizontal intensity at the place is calculated by the equation,

Bh = 2πnK x 10-7/r