The sensitivity of a moving coil galvanometer can be increased by decreasing
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → restoring couple per unit twist of suspension wire
The current sensitivity of a moving coil galvanometer is the deflection per unit current.
\( \displaystyle \frac{\phi}{I} = \frac{N B A}{k} \)
Here \( N \) is the number of turns, \( B \) the magnetic field, \( A \) the area of the coil and \( k \) the restoring couple per unit twist. The sensitivity rises when the numerator increases or the denominator decreases.
NCERT (2026-27):
The Moving Coil Galvanometer – “… In equilibrium
\( \displaystyle k\phi = NI AB \)
where k is the torsional constant of the spring; i.e. the restoring torque per unit twist.”
The Moving Coil Galvanometer – “… We define the current sensitivity of the galvanometer as the deflection per unit current. From Eq. (4.26) this current sensitivity is,
\( \displaystyle \frac{\phi}{I} = \frac{NAB}{k} \qquad (4.27) \)”