Name: Conversion of a Galvanometer Into a Voltmeter
Uploaded: 2019-07-19
Duration: 7 min 18 s
Description: This video helps us understand the working of a galvanometer. It also teaches us how to convert it into a voltmeter of the desired range both theoretically a...

Question

With the help of neat diagram, describe construction, theory and working of a moving coil galvanometer.

Accepted Answer

Construction:

A moving coil galvanometer consists of a rectangular coil with a large number of turns of thin insulated copper wire. The coil is suspended between the two poles of a strong magnet such as a horseshoe magnet. The lower end of the coil is connected to a hairspring having only a few turns.

The other end of the spring is connected to a binding screw. The coil consists of a soft iron cylinder placed symmetrically inside it. The hemispherical magnetic poles produce a radial magnetic field in which the plane of the coil is parallel to the magnetic field in all its positions. A small plane mirror is attached to the suspension wire along with a lamp and scale arrangement to measure the deflection of the coil.

Working:
Say, the area of the loop is $A$ .
The magnetic field is $B$ .
The number of turns in the coil is $N$ .
The current in the coil is $I$ .
The torque acting on the coil will be equal to, $τ = N I A B$
Say, the twist constant on the coil is $C$ .
Then the deviation of the coil is given by, $θ = \frac{τ}{C} = \frac{N I A B}{C}$
Therefore, $I = \frac{C θ}{N A B}$
Hence, the angle of deviation can give the value of the current flowing through the coil.

With the help of neat diagram, describe construction, theory and working of a moving coil galvanometer.

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