Question

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

Answer 1

Given: The resistance of the galvanometer coil is 12 Ω, the current at which the galvanometer shows full scale deflection is 3 mA and the range of the voltmeter is 0 to 18 V.

To convert a galvanometer into voltmeter a resistor has to be connected in series with the galvanometer.

The required resistance is given as,

R= V I g −G

By substituting the values in above equation, we get

R= 18 3× 10 −3 −12 =6000−12 =5988 Ω

Thus, the resistance of resistor which has to be connected in series with the galvanometer is 5988 Ω.