Question

How to increase voltage sensitivity in moving coil galvanometer?

Answer 1

Increase the turns on the coil. - Increase the electromagnetic field strength that produces the torque on the movement, deflecting the pointer.Use a more powerful magnet. ...Use a smaller taut band or hair spring. 

Answer 2

Voltage Sensitivity = ϕ/V = (NAB/KR) where

ϕ is the angular displacement, i.e. the reading you see on the galvanometer

V is, of course, the voltage across the galvanometer for which the reading is ϕ.

N is the number of turns of the moving-coil in the galvanometer.

A is the length of the rectangular-coil, B is the breadth of the rectangular-coil,

therefore AB represents the area of the 2D-coil.

K is the torsion-constant of the galvanometer, i.e., the spring-constant of the spring that's used in the galvanometer.

R is the resistance of the coil.

Now, increasing the number of turns N of the coil will result in the same increase in the resistance of the coil R as R∝l and surface-area of coil is kept constant.

Therefore, increasing number of turns N of the coil DOES NOT AFFECT the voltage-sensitivity of the galvanometer.

Therefore, in order to increase the voltage-sensitivity of the galvanometer,

1. you can increase the area of the coil

2. you can decrease the torsion-constant of the galvanometer.