Question

A moving coil galvanometer allows a full scale current of ${10}^{-4}A$. A series resistance of $2M\Omega$ is required to convert the above galvanometer into a voltmeter of range $0-5V$. therefore the value of shunt resistance required to convert the above galvanometer into an ammeter of range $0-10mA$ is:

• A. $40\Omega$
• B. $100\Omega$
• C. $10\Omega$
• D. $500\Omega$

Answer 1

The correct option is A $40\Omega$

$s^{\prime }=\left[\frac{Ig}{2I-Ig}\right]G$

$=\frac{(I-Ig)}{Ig}$=$\frac{g}{s}$

$I=Ig(\frac{G}{s}+1)$

$2I-Ig=2Ig\left(\frac{G}{s}\right)+Ig$

$200+{10}^{-4}G=5$

$200G=5$

$\frac{200}{5}=G$

$40\Omega$