question_answer

In the circuit, the galvanometer G shows zero deflection. If the batteries A and B have negligible internal resistance, the value of the resistor R will be                            [AIEEE 2005]

A) \[200\,\Omega \]

B) \[100\,\Omega \]

C) \[500\,\Omega \]

D) \[1000\,\Omega \]

Correct Answer: B

Solution :

[b] The galvanometer shows zero deflection i.e., current throughis zero.

As a result potential drop acrossis 2V, circuit can be redrawn as

\[l=\frac{12}{500+R}\]

Voltage across R,

\[V=lR\]

\[\Rightarrow \,\,2=\frac{12}{500+R}\times R\]

\[\Rightarrow \,\,1000\,+2R=12R\,\Rightarrow R=100\Omega \]