The total length of potentiometer wire AB is 50 cm in the arrangement as shown in figure. If $P$ is

Question

The total length of potentiometer wire AB is 50 cm in the arrangement as shown in figure. If $P$ is the point where the galvanometer shows zero reading then the length $A P$ is $\_\_\_\_$ cm.

Professor PC Thomas Classes · Answer

In a potentiometer, the potential drop across a length $l$ of the wire is proportional to the length, $V \propto l$. At the null point, the EMF of the cell in the secondary circuit is perfectly balanced by the potential drop across length $A P$. Applying the principle of the potentiometer $E = k \cdot l_{AP}$ and using the specific values given in the circuit diagram, the balancing length is derived as $AP = 30	ext{ cm}$.