Answer 1

The sensitivity (i.e. current sensitivity) of a galvanometer is defined as the angle of deflection per unit current flowing through it.
If dθ is change in the deflection produced by a small change in the current dI, sensitivity (S) of the galvanometer is given by

`S=(d theta)/(dI)`

The current I flowing through a moving coil galvanomet er is given by

`I=k/(nAB)theta` where θ is the angle of deflection , N is its turns, A is area, B is magnetic induction & k is the couple per unit twist.

`theta = (NAB)/k I`

`(d theta)/(dI)=(NAB)/k`

`S=(NAB)/k`