Question

A moving coil galvanometer of resistance $100\Omega$ is used as an ammeter using a resistance of $0.1\Omega$. The maximum deflection current in the galvanometer is $0.1\text{mA}$. Find the maximum current that can be measured using the ammeter.

• A. $100.01\text{mA}$
• B. $1000.1\text{mA}$
• C. $10.1\text{mA}$
• D. $1.01\text{mA}$

Answer 1

The correct option is A $100.01\text{mA}$

Let current flowing through the shunt resistance is $I-I_g$



Given that $G=100\Omega$
Shunt resistance, $\left(S\right)=0.1\Omega$
$I_g=0.1\text{mA}={10}^{-4}\text{A}$

From the fig.

$(I-I_g)S=I_{g}G$

$\Rightarrow I=I_g\frac{(G+S)}{S}=I_g(\frac{G}{S}+1)$

$I={10}^{-4}(\frac{100}{0.1}+1)=1000.1\times {10}^{-4}\text{A}$

$I=100.01\text{mA}$

Hence, $\left(A\right)$ is the correct answer.