question_answer

The deflection in a moving coil galvanometer falls from 50 divisions to 10 divisions when a shunt of\[12\,\Omega \]is applied. What is the resistance of the galvanometer?

A)  \[24\,\,\Omega \]                                          

B) \[48\,\,\Omega \]

C)  \[12\,\,\Omega \]                                          

D) \[36\,\,\Omega \]

Correct Answer: B

Solution :

                 In case of galvanometer, \[I\propto \theta \] So,          \[\frac{{{I}_{G}}}{I}=\frac{10}{50}=\frac{1}{5}\]i.e., \[{{I}_{G}}=\frac{1}{5}I\] Now as in case of a shunted galvanometer as shown                 \[(I-{{I}_{G}})S={{I}_{G}}G\] i.e.,        \[\left( I-\frac{1}{5}I \right)\times 12=\frac{1}{2}{{I}_{G}}\] \[\therefore \]  \[G=4\times 12=48\,\Omega \]