Question

A moving coil galvanometer of resistance 20 Ω gives a full scale deflection when a current of 1 mA is passed through it. It is to be converted into an ammeter reading 20 A on full scale deflection. If a shunt wire of 0.005 only is available, then what resistance should be connected in series with the galvanometer coil?

Options

• 99.955 Ω

• 79.995 Ω

• 59.295 Ω

• 19.955 Ω

Answer 1

79.995 Ω

Explanation:

Using, `i_g = i S/(S + (G + R))`

`10^-3 = 20 (0.005/(0.005 + 20 + R))`

R = 79.995 Ω