Question

A galvanometer has coil resistance $100\Omega$ and gives a full scale deflection for $30\text{mA}$ current . If it is to work as a voltmeter of $30\text{V}$ range, the resistance required to be added will be

• A. $1000\Omega$
• B. $900\Omega$
• C. $180\Omega$
• D. $500\Omega$

Answer 1

The correct option is B $900\Omega$

Voltmeter reading, $V=i(4+R)$
$\Rightarrow 30=\frac{30}{1000}(100+R)$
$\Rightarrow 1000=100+R$
$\therefore R=900\Omega$