Q. 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
A) 200$\Omega$
B) 100$\ \Omega$
C) 500$\ \Omega$
D) 1000$\ \Omega$
Explanation
(b) The galvanometer shows zero deflection $ie$, current through XY is zero.
As a result potential drop across R is 2V, circuit can be redrawn as
$I = \frac{12}{500 + R}$
Voltage across R, $V = IR$
$\Longrightarrow \ \ 2 = \frac{12}{500 + R} \times R$
$\Longrightarrow 1000 + 2R = 12R$
$\Longrightarrow R = 100\Omega$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.