Question

Consider the potentiometer circuit shown in the figure below. The potentiometer wire is 600 cm long. At what distance from point A should the jockey be placed to get zero deflection in the galvanometer?

• A. 320 cm
• B. 500 cm
• C. 250 cm
• D. 430 cm

Answer 1

The correct option is A

320 cm

For zero deflection of the galvanometer, no current will flow in the secondary circuit.
Current through the potentiometer wire, $I=\frac{E}{r+15r}=\frac{E}{16r}$
Suppose the distance from end A where the jockey is placed be $x$ cm. The drop across this length of potentiometer wire will be $\frac{E}{2}$.
$\frac{E}{2}=I\times \frac{x}{600}\times 15r\Rightarrow \frac{E}{2}=\frac{E}{16r}\times \frac{x}{600}\times 15r\therefore x=320cm$