Question

The deflection in a galvanometer decreases from 25 divisions to 5 divisions when a resistor of 20$\Omega$ is connected in series. Find resistance of galvanometer.

• A. 4 $\Omega$
• B. 5 $\Omega$
• C. 6 $\Omega$
• D. 7 $\Omega$

Answer 1

The correct option is B 5 $\Omega$

When resistor $20\Omega$ is not connected,
Using $V=IR,$ we get $V=25R_G...\left(1\right)$ where $R_G=$ resistance of galvanometer.
When resistor $20\Omega$ is connected,
$V=5(20+R_G)...\left(2\right)$
Using (1), $25R_G=5(20+R_G)$
$\Rightarrow 5R_G=20+R_G$
$\Rightarrow 4R_G=20\Rightarrow R_G=5\Omega$