CUET · PHYSICS · PYQ PAPER 2023

Two charges \( q_1 = 4 \times 10^{-7} \text{ C} \) and \( q_2 = -6 \times 10^{-7} \text{ C} \) are located 3 m apart. At what point on the line joining the two charges is the electric potential zero? (Consider potential zero at infinity.)

A 1.5 meter from charge \( q_1 \)
B 1.5 meter from charge \( q_2 \)
C 1.2 meter from charge \( q_1 \)
D 1.2 meter from charge \( q_2 \)

Verified Solution

Answer & Solution

Correct Answer

(C) 1.2 meter from charge \( q_1 \)

Step-by-step Solution

Detailed explanation

\( V = V_1 + V_2 = 0 \) \( k\frac{q_1}{x} + k\frac{q_2}{d-x} = 0 \) \( \frac{q_1}{x} = -\frac{q_2}{d-x} \) \( q_1(d-x) = -q_2 x \) \( (4 \times 10^{-7})(3-x) = -(-6 \times 10^{-7})x \) \( 4(3-x) = 6x \) \( 12 - 4x = 6x \) \( 12 = 10x \) \( x = 1.2 \text{ m} \)

Apply the relevant identity from the chapter and substitute the values established in the previous step, keeping the original constraint in view.

Use the simplified expression to isolate the unknown, then plug the result back into the question setup to confirm the working is internally consistent.

Cross-check against a boundary or limiting case. Both the dimensional balance and the qualitative behaviour at the extreme should agree with the candidate answer.

Combine the steps above to identify the correct option. The remaining choices each fail at least one of the consistency, dimensional, or boundary checks.

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