Question

A galvanometer having a resistance $12\Omega$ gives a full scale deflection for a current of $2.5mA.$ It is converted in to a voltmeter of range $10V$ , what is the net resistance of meter ?

• A. $3898\Omega$
• B. $4000\Omega$
• C. $4\Omega$
• D. $0.25\Omega$

Answer 1

The correct option is B $4000\Omega$

Additional resistance required
$R=\frac{V}{I_0}-G$
$=\frac{10}{2.5\times {10}^{-3}}-12$
$=4000-12=3988\Omega$
Since $R$ is connected in series , so net resistance of meter
$R+G$
$3988+12=4000\Omega$