Question

A galvanometer of resistance $200$ ohm gives a full scale deflection for a current of $5$ mA. How will you use it to measure potential differences upto $10$V.?

Answer 1

Galvanometer is a very sensitive instrument which cannot measure high potential difference (in this case a potential difference of 10 V). So we convert the Galvanometer into voltmeter by connecting a very high resistance in series connection with the galvanometer.

Making use of the formula:

V= I g (R g + R x)

Given Potential difference= 10 V; Galvanometer current I g= 5 m A = .005 A and Galvanometer resistance= 200 Ohm.

R x= High resistance to convert galvanometer to voltmeter.

(10 v/ .005 A) - 200 ohm = R x

R x= 1800 ohm.

So to measure a potential difference of 10 v we have to connect a resistance of 1800 ohm in series with the galvanometer.