Question

A moving coil galvanometer has a coil of resistance $59\Omega$. It shows a full scale deflection for a current of $50$mA. How will you convert it to an ammeter having a range of $0$ to $3$A?

Answer 1

A moving coil galvanometer is converted by connecting a shunt resistance $R_s$ in parallel to galvanometer resistance $R_G$.

Given : $I=3A$, $R_G=59\Omega$ and $I_G=0.05A$

Since potential difference A and B is equal to that between C and D.

$\therefore$ $I_G{R}_G=(I-I_G)R_s$

Or $\left(0.05\right)\left(59\right)=(3-0.05)R_s$

$⟹$ $R_s=1\Omega$