CUET · PHYSICS · PYQ PAPER 2025

Two coaxial solenoids having number of turns per unit length 50 and 200, respectively, have same length 50 cm. The area of cross-section of the two solenoids are \( 4 \, \text{cm}^2 \) and \( 6 \, \text{cm}^2 \), respectively. The mutual inductance of the two solenoids is:

A \( 8\pi \times 10^{-3} \, \text{H} \)
B \( 4\pi \times 10^{-4} \, \text{H} \)
C \( 8\pi \times 10^{-7} \, \text{H} \)
D \( 1.6\pi \times 10^{-2} \, \text{H} \)

Verified Solution

Answer & Solution

Correct Answer

(A) \( 8\pi \times 10^{-3} \, \text{H} \)

Step-by-step Solution

Detailed explanation

\(M=\frac{4 \pi \times 10^{-7} \times 50 \times 200 \times 4.9 \times 10^{-4}}{0.5}\) \(M=\frac{4 \pi \times 10^{-7} \times 50 \times 200 \times 4.9 \times 10^{-4}}{0.5}=8 \pi \times 10^{-3} H\) \(8 \pi \times 10^{-3} H\).

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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