Question

In meter bridge experiment, null point was obtained at a distance \( f \) from left end. The values of resistances in the left and right gaps are doubled and then interchanged. The new position of null point is

• A. \( 100 - \ell \)
• B. \( 100 - \frac{\ell}{4} \)
• C. \( 100 - \frac{\ell}{2} \)
• D. \( 100 - 2\ell \)

Hint:

In meter bridge experiments, when resistances are altered, the null point shifts in such a way that the ratio of the resistances is still balanced.

Answer 1

The Correct Option is A

Step 1: Understanding the meter bridge principle.
In the meter bridge experiment, the null point is determined using a known resistance \( R_1 \) and an unknown resistance \( R_2 \) in the two gaps. The position \( \ell \) corresponds to the balancing point where the ratio of the resistances is equal. The position of the null point is given by: \[ \frac{R_1}{R_2} = \frac{\ell}{100 - \ell} \] Step 2: Applying changes to the resistances.
When the resistances are doubled and interchanged, the new null point will still satisfy the same principle, but the values of the resistances change. After the modifications, the new null point position is \( 100 - \ell \), corresponding to option (A).
Step 3: Conclusion.
Thus, the new position of the null point is \( 100 - \ell \), corresponding to option (A).