Question

A moving coil galvanometer has $50$ turns and each turn has an area $2\times {10}^{-4}{m}^2$. The magnetic field produced by the magnet inside the galvanometer is $0.02$ T. The torsional constant of the suspension wire is ${10}^{-4}$ Nm rad${}^{-1}$. When a current flows through the galvanometer, a full-scale deflection occurs if the coil rotates by $0.2$ rad. The resistance of the coil of the galvanometer is $50\Omega$. This galvanometer is to be converted into an ammeter capable of measuring current in the range 0 - 1.0 A. For this purpose, a shunt resistance is to be added in parallel to the galvanometer. The value of this shunt resistance, in ohms, is ________.

Answer 1

$n=50$ turns, $A=2\times {10}^{-4}{m}^2$

$B=0.02$T K = ${10}^{-4}$

$Q_m=0.2$rad $R_g=50\Omega$

$I_A=0–1.0A$ $T=MB=C\theta ,M=nIA$

$BINA=C\theta$

$0.02\times 1\times 50\times 2\times {10}^{-4}={10}^{-4}\times 0.210$

$I_g=0.1A$

For galvanometer, resistance is to be connected to ammeter in shunt.

$I_g\times R_g=(I–I_g)S$

$0.1\times 50=(1–0.1)S$

$S=\frac{50}{9}=5.55$