Question

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

1 $\Omega$ in parallel

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 $I=5A$,

$\therefore \frac{1/60}{5-\left(1/60\right)}=\frac{S}{300}$ $\Rightarrow S=1\Omega$