Question

A galvanometer has a resistance of 30Ω, and its full-scale deflection current is 20 microampere (μA). What resistance should be added to it to have a range of 0-10 volts?

Answer 1

Given:

G = 30 W,

V = 10 V

l_g = 20 µA = 20 × 10⁻⁶ A

To find:

Resistance (R) added to read voltage 10 V = ?

Formula:

`R = V/I_g - G`

`R = 10/(20 xx 10^-6) - 30`

= 0.5 × 10⁶ − 30

= 500000 − 30

∴ R = 499970 Ω

By connecting 499970 Ω resistance in series with a galvanometer, we can convert the galvanometer into a voltmeter to read voltage up to 10 V.