Question

A galvanometer has a resistance of 50 Ω  and a current of 2 mA is needed for its full scale deflection. Calculate the resistance required to convert it into an ammeter of 0.5 A range.

Answer 1

Given:

Resistance of Galvanometer = R_g = 50 Ω

Full scale deflection current = I_g = 2 mA  = 2 × 10⁻³ A

Ammeter range = I = 0.5 A

Formula:

To convert a galvanometer into an ammeter, a shunt resistance (R_s​) is connected in parallel with it. The shunt resistance is given by:

`R_s = (I_g R_g)/(I - I_g)`

`R_s = (2 xx 10^(-3) xx 50)/(0.5 - 2 xx 10^(-3))`

⇒ `R_s = (0.1)/0.498`

⇒ R_s = 0.201 Ω

∴ The required shunt resistance is 0.201 Ω.