Question

A galvanometer gives full scale deflection with 0.006 A current. By connecting it to a 4990 $\Omega$ resistance, it can be converted into a voltmeter of range 0-30 V. If connected to a $\frac{2n}{249}\Omega$ resistance, it becomes an ammeter of range 0 - 1.5 A. The value of $n$ is :

Answer 1

$I_g=0.006AI=1.5A$

$S=\frac{2n}{249}R=4990$

$V=30v$

$V_{AB}=V_{CD}$

$\left(\frac{I-I_g}{I_g}\right)G=\frac{v}{I_g}-R$

$\left(\frac{1.5-0.006}{0.006}\right)\times \frac{2n}{249}=\frac{30}{0.006}-4990$

$\frac{1.494}{0.006}\times \frac{2n}{249}=\frac{30-29.94}{0.006}$

$\frac{1.494\times 2n}{249}=0.06$

$n=\frac{0.06\times 249}{1.494\times 2}$

$n=\frac{14.94\times 1000}{1.494\times 2\times 2\times 100}$

$n=5$