Ray Optics: Total Reflection Prism Application MCQ

Solve this quality-checked JEE multiple-choice question, then review the correct answer and explanation.

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Total Reflection Prism ApplicationHardQuestion 20249

Question

A 45°-45°-90° glass prism (n=1.5) is used to deviate light by 90° using TIR. This works because:

A
45° > critical angle for n=1.5
Correct
B
45° < critical angle for n=1.5, allowing TIR
C
n=1.5 gives critical angle of 30°
D
The 90° face acts as a lens

Correct answer

45° > critical angle for n=1.5

Explanation

Critical angle for n=1.5: sin θ_c = 1/1.5 = 2/3 → θ_c ≈ 41.8°. When light hits the hypotenuse at 45° (> 41.8°), TIR occurs → light is deviated 90°. Used in periscopes, binoculars, and retroreflectors.

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