Question

A potentiometer wire is 4m long and potential difference of 3V is maintained between the ends. The e.m.f. of the cell which balances against a length of 100 cm of the potentiometer wire is

• A. \(0.75\) V
• B. \(0.5\) V
• C. \(0.25\) V
• D. \(1.5\) V

Hint:

Potential gradient is 3 V per 4 m; multiply by 1 m.

Answer 1

The Correct Option is A

Step 1: Fraction of the wire:
100 cm is $\dfrac14$ of the 400 cm wire.

Step 2: Fraction of voltage:
The potential drop over that part is $\dfrac14\times3$ V.

Step 3: Result:
$0.75$ V, option (A).

Final Answer:
The cell has emf 0.75 V. \[ \boxed{\text{(A) }0.75\ \text{V}} \]