Question

A galvanometer has a resistance of $20\Omega$ and reads full-scale when $0.2V$ is applied across it. To convert it into a $10A$ ammeter, the galvanometer coil should have a

• A. $0.01\Omega$ resistor connected across it.
• B. $0.02\Omega$ resistor connected across it.
• C. $200\Omega$ resistor connected across it.
• D. $2000\Omega$ resistor connected across it.

Answer 1

Answer: (B)

$0.02\Omega$ resistor connected across it.

Given, $V=0.2V$, $R_g=20\Omega$ and $I=10A$.

Hence,
$I_g=\frac{0.2}{2}=0.01A$

To convert galvanometer into a 10A ammeter, the galvanometer coil should have to connect a shunt resistance in parallel, given by

$S=\frac{R_g{I}_g}{I-I_g}$

$S=\frac{\left(20\right)\left(0.01\right)}{10-0.01}$

$S=\frac{0.2}{9.99}=0.02A$