A = area of cross-section of the coil and θ = angle of twist.
Current Sensitivity
The deflection produced per unit current in galvanometer is called its current sensitivity. Current sensitivity I s = θ / I = NBA / K
Voltage Sensitivity
The deflection produced per unit voltage applied across the ends of galvanometer is called its voltage sensitivity.
Voltage sensitivity
V s = θ / V = NBA / KR where R is the resistance of the galvanometer. Therefore for a sensitive galvanometer
( i) N should be large( ii) B should be large( iii) A should be large( iv) K should be small
Ammeter
An ammeter is a low resistance galvanometer used for measuring the current in a circuit. It is always connected in series.
Conversion of a Galvanometer into an Ammeter
A galvanometer can be converted into an ammeter by connecting a low resistance into its parallel.
If G is the resistance of a galvanometer and it give full scale deflection for current,
I g then required low resistance S, connected in its parallel for converting it into an ammeter of range I is given by