CUET · PHYSICS · PYQ PAPER 2025

A ray of light from air passes through an equilateral triangular glass prism and undergoes minimum deviation when the angle of incidence is 3/4 of the angle of prism. The speed of light in the prism is :

A \( 1.15 \times 10^8 \text{ m/s} \)
B \( 2.12 \times 10^8 \text{ m/s} \)
C \( 2.78 \times 10^8 \text{ m/s} \)
D \( 3 \times 10^8 \text{ m/s} \)

Verified Solution

Answer & Solution

Correct Answer

(B) \( 2.12 \times 10^8 \text{ m/s} \)

Step-by-step Solution

Detailed explanation

\( A = 60^\circ \) \( i = \frac{3}{4}A = \frac{3}{4}(60^\circ) = 45^\circ \) \( \delta_m = 2i - A = 2(45^\circ) - 60^\circ = 30^\circ \)…

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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