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  Solved  Paper-2005

A) \[200\,\Omega \]     

B)       \[100\,\Omega \]            

C)        \[500\,\Omega \]           

D)        \[1000\,\Omega \]

Correct Answer: B

Solution :

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, \[V=lR\] \[\Rightarrow \,\,2=\frac{12}{500+R}\times R\] \[\Rightarrow \,\,1000\,+2R=12R\,\Rightarrow R=100\Omega \]