The galvanometer deflection, when key \[{{K}_{1}}\]is closed but \[{{K}_{2}}\] is open, equals \[{{\theta }_{0}},\] (see figure). On closing \[{{K}_{2}}\]also and adjusting \[{{R}_{2}}\] to \[5\Omega ,\]the deflection in galvanometer becomes\[\frac{{{\theta }_{0}}}{5}.\] The resistance of the galvanometer is, then, given by [Neglect the internal resistance of battery] [JEE Main 12-Jan-2019 Morning] |
A) \[25\Omega \]
B) \[22\Omega \]
C) \[5\Omega \]
D) \[12\Omega \]
Correct Answer: B
Solution :
[b] Initially, let be the current through G. |
then |
After the key is closed, the circuit is shown as Apply KVL on loop 1, |
Also, |
For a galvanometer, |
So, |
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