Question

In potentiometer experiment, null point is obtained at a particular point for a cell on potentiometer wire 'x' cm long. If length of potentiometer wire is increased by few cm without changing the cell, the balancing length will (Driving source is not changed)

• A. decrease
• B. increase
• C. not change
• D. become zero

Hint:

The potential gradient falls when the wire becomes longer, so the balancing length increases.

Answer 1

The Correct Option is B

Step 1: Use E = k l:
The cell emf $E$ is fixed. At balance, $E=k\,l$.

Step 2: Track k:
A longer wire has a larger resistance, so the current from the driving source falls, and the potential drop per unit length ($k=IR/L$) falls.

Step 3: Conclude:
For fixed $E$, a smaller $k$ needs a larger $l$, so the balancing length increases. Option B.

Final Answer:
A longer wire lowers the potential gradient, so the null point moves farther. \[ \boxed{\text{(B) }\text{increase}} \]