Question

A moving coil galvanometer has 150 equal divisions. Its current sensitivity is 10-divisions per milliampere and voltage sensitivity is 2 division per millivolt. In order that division reads 1 Volt, the resistance in ohm needed to be connected in series with the coil will be:

• A. 100000
• B. 1000
• C. 9995
• D. 99995

Answer 1

The correct option is C 9995

$V_{max}=\frac{150}{2}=75mV$

$I_{max}=\frac{150}{10}=15mA=Ig$

Resistance of Galvanometer $G=\frac{75}{15}$

$G=5\Omega$

For conversion into a voltmeter, a high resistance should be connected in series with the galvanometer.

$V=Ig(G+R)$

$150=\frac{15}{1000}(5+R)$

$10=\frac{5+R}{1000}$

$5+R=10000$

$\therefore R=9995\Omega$