Question

In a potentiometer circuit when two cells of e.m.f. \(1.5\) volt and \(1.2\) volt are connected to assist each other, balancing length is \(270\) cm. What will be the balancing length in cm when these two cells are connected in opposition?

• A. \(90\)
• B. \(81\)
• C. \(60\)
• D. \(30\)

Hint:

Balancing length is proportional to the net e.m.f.

Answer 1

The Correct Option is D

Step 1: Ratio Method:
$\dfrac{l_2}{l_1}=\dfrac{E_1-E_2}{E_1+E_2}=\dfrac{0.3}{2.7}=\dfrac19$.

Step 2: Compute:
$l_2=\dfrac{270}9=30$ cm.

Step 3: Answer:
Option (D).

Final Answer:
Option (D). \[ \boxed{\text{(D) } 30\ \text{cm}} \]