question_answer

The deflection in a moving coil galvanometer falls from 50 divisions to 10 divisions, when a shunt of \[12\,\,\Omega \] is connected with it. The resistance of galvanometer coil is

A)  240                                       

B)  120             

C)  60                                         

D)  480

Correct Answer: D

Solution :

 Let the value of current for one division of galvanometer is i. Then, the current through the ammeter \[(I)=50i\] and current through the galvanometer \[({{I}_{g}})=10i\] As we know that, \[S=\frac{{{I}_{g}}}{(I-{{I}_{g}})}G\] \[\Rightarrow \]               \[G=S\,\left( \frac{I-{{I}_{g}}}{{{I}_{g}}} \right)\] \[=12\times \,\left[ \frac{50i-10i}{10i} \right]\] \[=12\times \,\left[ \frac{40i}{10i} \right]=40\,\Omega \]