**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 B

_{h}, the earth horizontal intensity at the place, then according to the tangent law, B = B_{h}tan θ; where θ is the mean deflection in the TG.
Therefore, μo/4π x 2πni/r = B

_{h}tan θ
i.e., 10

^{-7}x 2πni/r = B_{h}tan θ
i = (10

^{7}x B_{h}r/2πn) x tan θ ; i = K tan θ ; where K is called the reduction factor of TG.
Therefore, K = i/tan θ

But K = (10

^{7}x B_{h}r)/2πn
Therefore, B

_{h}= (2πnK/r) x 10^{-7}*(xiii) Procedure of Tangent Galvanometer Experiment*

Ans:

**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 θ

_{1}and θ_{2}at both ends of the pointer are noted. The current is reversed with the help of the commutator. Again the readings θ_{3}and θ_{4}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 B**

_{h}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,

**B**

_{h}= 2πnK x 10^{-7}/r
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