A moving coil galvanometer has a resistance of 4 ohms and gives full-scale deflection when carrying 30 milliamperes.

A moving coil galvanometer has a resistance of 4 ohms and gives full-scale deflection when carrying 30 milliamperes. The instruments can be used to measure 150 volts by connecting in series with the instrument a resistance of

Right Answer is:

4996 ohms

SOLUTION

The resistance of the galvanometer RG = 4Ω

Full-scale deflection Current IF = 30 mA = 30 × 10−3A

Voltmeter Range V = 150 V

Let a resistor of resistance R be connected in series with the galvanometer to convert it into a voltmeter. This resistance is given as:

R = V/IF

= 150/30 × 10−3 = 5000V

Hence the value of resistance to be connected in series

RG − R = 5000 − 4 = 4996Ω

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