Three moving coil galvanometers A, B and C are made of coils of three different material having torsional constant $1.8 imes 10^{- 8},\ 2.8 imes 10^{- 8}$ and $3.8 imes 10^{- 8}$ respectively. If the three galvanometers are identical in all other respect, then in which of the above cases sensitivity is maximum?

Question

Three moving coil galvanometers A, B and C are made of coils of three different material having torsional constant $1.8 	imes 10^{- 8},\ 2.8 	imes 10^{- 8}$ and $3.8 	imes 10^{- 8}$ respectively. If the three galvanometers are identical in all other respect, then in which of the above cases sensitivity is maximum?

Dr. Abubacker · Accepted Answer

(a) Current sensitivity of a galvanometer is defined as the deflection produced in the galvanometer when a unit current flows through it.
If $	heta$ is the deflection in the galvanometer when current $I$ is passed through it, then
$Current\ Sensitivity\ I_{s} = \frac{	heta}{I} = \frac{nBA}{k}$
where $k$ be restoring torque per unit twist, $n$ be number of turns in the coil, B is strength of magnetic field in which coil is suspended, A be area of coil.
Since, restoring per unit twist (torsional constant) is minimum for galvanometer A, hence more sensitive.

Explanation

Reviewed by Dr. Abubacker

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