question_answer

Directions : (36-40)

Conversion of Galvanometer to Voltmeter

A galvanometer can be converted into voltmeter of given range by connecting a suitable resistance \[{{R}_{s}}\] in series with the galvanometer, whose value is given by

\[{{R}_{s}}=\frac{V}{{{I}_{g}}}-G\]

where V is the voltage to be measured, \[{{I}_{g}}\] is the current for full scale deflection of galvanometer and G is the resistance of galvanometer.

Series resistor \[\left( {{R}_{s}} \right)\]increases range of voltmeter and the effective resistane of galvanometer. It also protects the galvanometer from damage due to large current.

Voltmeter is a high resistance instrument and it is always connected in parallel with the circuit element across which potential difference is to be measured. An ideal voltmeter has infinite resistance.

In order to increase the range of voltmeter n times the value of resistance to be connected in series with galvanometer is \[{{R}_{s}}=\left( n-1 \right)G\].

10 mA current can pass through a galvanometer of resistance\[25\Omega \]. What resistanfe in series should be connected through it, so that is it converted into a voltmeter of 100 ?

A) \[0\centerdot 975\Omega \]

B) \[99\centerdot 75\Omega \]

C) \[975\Omega \]

D) \[99\,75\,\Omega \]