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Tangent Galvanometer Viva Questions


Tangent Galvanometer Experiment Viva Questions

(1) What is meant by a tangent galvanometer?

 

A tangent galvanometer is a moving magnet type galvanometer and is used for measuring strength of electric current.

 

(2) What is tangent law?

 

If Bh and B be two magnetic fields acting perpendicular to each other, and their resultant makes an angle θ with Bh,

tan θ = (B/Bh);

Therefore, B = Bh tan θ

 

(3) What is magnetic meridian?

 

Magnetic meridian is a vertical plane passing through the magnetic axis (axial line) of a freely suspended or pivoted magnetic needle.

 

(4) Why is the pointer long and made of aluminium?

 

Aluminium makes pointer light. Moreover, aluminium is non-magnetic.

 

(5) What is the function of the plane mirror at the bottom of the compass box?

 

It helps in reading the position of the pointer on the scale without error of parallax.

 

(6) Define reduction factor of T.G.

 

Reduction factor of T.G. is defined as that current which when passed through the galvanometer required to produce a deflection of 45° when set in magnetic meridian.

 

(7) What are the two perpendicular magnetic fields in T.G. experiment?

 

The horizontal component of earth's magnetic field and the field produced by the current carrying circular coil.

 

(8) Why the deflection in tangent galvanometer is preferred to be nearly 45°?

 

An error in the measurement of θ will affect the result as tangent of θ. When θ is nearly 45° the variation in tan θ is very small and hence a small error in measurement of θ will cause negligible error.


(9) Aim of Tangent Galvanometer Experiment

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

(10) 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.

(11) 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

(12) 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 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

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