Question

The range of voltmeter of resistance $300\Omega$ is $5V$. The resistance to be connected to convert it into an'ammeter of range $5A$ is

• A. $1\Omega$ in series
• B. $1\Omega$ in parallel
• C. $0.1\Omega$ in series
• D. $0.1\Omega$ in parallel

Answer 1

Answer: (B)

A voltmeter is a galvanometer having a high resistance connected in series with it. The current through the galvanometer
is $I_g=\frac{5V}{300\Omega }=\frac{1}{60}A$
An ammeter is a galvanometer having a low resistance connected in parallel with it. The shunt resistance $S$ is determined from
$\frac{I_g}{I-I_g}=\frac{S}{G}$
where $G=300\Omega$ (Given)
For $I=5A$, we get,
$\frac{1/60}{5-(1/60)}=\frac{S}{300}$
$\Rightarrow S=1\Omega$