Question

A galvanometer coil has a resistance of 12 Ω 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?

Answer 1

Resistance of the galvanometer coil, G = 12 Ω
Current for which there is full scale deflection,l, = 3 mA = 3 × 10⁻³ A Range of the voltmeter is 0, which needs to be converted to 18 V.
V = 18 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:

Hence, a resistor of resistance   is to be connected in series with the galvanometer.