question_answer

If resistance of voltmeter is \[10000\,\Omega \] and resistance of galvanometer is \[2\,\,\Omega ,\] then find R when voltmeter reads 12 V and galvanometer reads 0.1 A.

A)  \[118\,\,\Omega \]                                       

B)         \[120\,\,\Omega \]

C)         \[124\,\Omega \]                           

D)         \[114\,\Omega \]

Correct Answer: A

Solution :

The circuit diagram with current variation can be drawn as: Let current \[{{I}_{g}}\]flows through R and G. For a voltmeter with full scale reading, we have \[V={{I}_{g}}(G+R)\] or            \[R=\frac{V}{{{I}_{g}}}-G\] Given, \[G=2\Omega ,V=12\,volt,\,{{I}_{g}}=0.1\,A\] \[\therefore \]  \[R=\frac{12}{0.1}-2\]                                 \[=120-2\] \[=118\,\Omega \]