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

What is moving coil galvanometer? Draw labelled diagram of suspended coil galvanometer and prove that the deflection of a coil is directly proportional to the current flowing through it.

Accepted Answer

A moving coil galvanometer is an electromagnetic device that can measure small values of current. It is also known as the Weston galvanometer. A moving coil galvanometer operates on the principle of magnetic torque, which is experienced when a current-carrying coil is put in an external magnetic field.

The angle at which the coil is deflected due to the magnetic torque effect is proportional to the coil's current magnitude. Moving coil galvanometer consists of permanent horse-shoe magnets, coil, soft iron core, pivoted spring, non-metallic frame, scale and pointer.

When current ( $I$ ) is passed in the coil, torque $τ$ acts on the coil, given by $τ = N I A B \sin θ$ Where $θ$ is the angle between the normal to plane of coil and the magnetic field of strength $B, N$ is the number of turns in a coil.

When the magnetic field is radial, as in the case of cylindrical pole pieces and soft iron core, then in every position of coil the plane of the coil, is parallel to the magnetic field lines, so that $θ = 90 °$ and $\sin 90 ° = 1$ .

Deflecting torque, $τ = N I A B$

If $C$ is the torsional rigidity of the wire and θ is the twist of suspension strip,

Then restoring torque = $C θ$

For equilibrium,

deflecting torque = restoring torque

$N I A B = C θ θ = \frac{N A B}{C} I θ \propto I$

The deflection of coil is directly proportional to current flowing in the coil and hence we can construct a linear scale

Embibe Experts Solutions for Chapter: Moving Charges and Magnetism, Exercise 1: chhattisgarh board-2019

Embibe Experts Physics Solutions for Exercise - Embibe Experts Solutions for Chapter: Moving Charges and Magnetism, Exercise 1: chhattisgarh board-2019

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