A galvanometer coil has a resistance of 12 and the metre shows full scale deflection for a current of 3 mA. How will you convert the metre into a voltmeter of range 0 to 18 V?

Question

Philoid · Accepted Answer

Given:

Resistance of the galvanometer coil, G = 12Ω

Current for full scale deflection = 3mA

For converting a galvanometer into a Voltmeter we can connect a resistance in series with the galvanometer. A minimum value of current should be allowed to flow through the voltmeter.

Required range of the voltmeter = 0 to 18 V

V = 18

Let the resistance needed = R_s

…(1)

By plugging the values of V, G and I_s in equation 1, we get,

⇒

⇒ R_s = 5988 Ω

For converting the galvanometer into a voltmeter of range 0-18 we can add a resistance of 5988Ω, is series with the galvanometer.