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 $\frac{2n}{249}\Omega$ a resistance, it becomes an ammeter of range 0 – 1.5 A. The value of n is

Answer 1

For voltmeter : $T_g=0.006A,R=4990\Omega ,V=30V$
$V=I_g(R_g+R)$

$30=0.006(R_g+4990)$

$R_g+4990=\frac{30\times 1000}{6}=5000$

$R_g=10\Omega$

For ammeter : $I=1.5A,R_g=10\Omega$

$L_g{R}_g=(I-I_g)R_s$

$0.006\times 10=(1.5-0.006)\times \frac{2n}{249}$

$n=\frac{0.06\times 249}{1.494\times 2}=5.$