A ray of light traveling from glass into ethyl alcohol is incident at the boundary at an angle of incidence 30…

Analyze the question: Light moves from glass (n = 1.5) into ethyl alcohol (n = 1.36). Since alcohol is optically less dense, the ray bends away from the normal, so the angle of refraction must be greater than 30°.

Concept: Snell's law: n₁ sin i = n₂ sin r

Solution:

1.5 × sin 30° = 1.36 × sin r

1.5 × 0.5 = 1.36 × sin r

0.75 = 1.36 × sin r

sin r = 0.75 / 1.36 = 0.5515

r = sin⁻¹(0.5515) ≈ 33.5°

Check: sin 33.5° = 0.5519, which matches.

Check against the options:

• A (27°) is less than 30°, which is wrong because the ray should bend away from the normal.
• C (51.7°) and D (72.8°) are too large.
• B (33.5°) matches the calculation.

Tip: Before calculating, check the direction of bending. Going from a higher index to a lower index means r > i (away from the normal), and going from a lower index to a higher index means r < i (towards the normal). This can eliminate options quickly. Also remember that sin 30° = 0.5 makes the calculation easy.