The current sensitivity of a galvanometer can be increased by :
(A) decreasing the number of turns
(B) increasing the magnetic field
(C) decreasing the area of the coil
(D) decreasing the torsional constant of the spring
Choose the most appropriate answer from the options given below :

Solution

Physics sir · 2 steps

Write the sensitivity formula first, then check which way each change moves it.

1. Balance the torques. At steady deflection, the magnetic torque on the coil equals the restoring torque of the spring: NIAB = kφ. Current sensitivity is the deflection per unit current.

   φ/I = NAB/k

   Change	Effect on NAB/k	Sensitivity
   (A) fewer turns N	numerator falls	decreases
   (B) larger field B	numerator rises	increases
   (C) smaller area A	numerator falls	decreases
   (D) smaller torsional constant k	denominator falls	increases

2. So. Only (B) and (D) raise the current sensitivity, which is option (d).

The idea to keep. Current sensitivity is NAB/k. Anything that makes the coil turn harder (N, A, B) or makes the spring softer (k smaller) raises it.

Answer from the NTA final answer key. Solution by PrepWiser.