The current sensitivity of a moving coil galvanometer can be increased by:
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → having a spring of lower torsional constant
Current sensitivity is the deflection per unit current. In equilibrium the magnetic torque \( NIAB \) is balanced by the restoring torque \( k\phi \) of the spring.
\( \displaystyle NIAB = k\phi \)
\( \displaystyle \frac{\phi}{I} = \frac{NAB}{k} \)
A spring of lower torsional constant k gives a larger deflection for the same current.
NCERT (2026-27):
The Moving Coil Galvanometer – “… In equilibrium
\( \displaystyle k\phi = NIAB \)
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,
\( \displaystyle \frac{\phi}{I} = \frac{NAB}{k} \qquad (4.27) \)”