Question

A galvanometer of resistance $25\Omega$ shows a deflection of $5$ divisions when a current of $2mA$ is passed through it. If a shunt of $4\Omega$ is connected and there are $20$ divisions on the scale, then the range of the galvanometer is

• A. $1A$
• B. $58A$
• C. $58mA$
• D. $30mA$

Answer 1

Answer: (C)

$58mA$

There are $20$ divisions on scale.
Initially, current for $20$ divisions $=\frac{2\times 20}{5}=8mA$
$\therefore I_g=8mA$
$\because \frac{I_g}{I}=\frac{S}{S+G}$
$\Rightarrow I=\left(\frac{S+G}{S}\right)I_g\Rightarrow I=\left(\frac{4+25}{4}\right)\times 8$
$=29\times 2=58mA$