Question

A galvanometer is converted in to voltmeter to increase its range by a factor of 40. If the voltmeter resistance is 2000 ohm , the resistance of the galvanometer is

Answer 1

50 ohms is the resistance of the galvanometer.

Explanation:

• potentiometer is converted to voltmeter by adding a resistance in series.
• Let R be the resistance of the galvanometer and x be the series resistance added.
• Therefore the resistance of the voltmeter becomes $R+x= 2000$ ----(1)
• The voltage range changed by a factor of 40

⇒$\frac{R}{R+x} =\frac{1}{40}$-------(2) from the voltage drop across galvanometer before and after adding series resistance.

therefore, on solving (1) and (2) equations,

i.e., by substituting (1) in (2) we get, $\frac{R}{2000}= \frac{1}{40}$

⇒$R=50$ohms

Therefore, the resistance of the galvanometer is 50 ohms.