Question

    A ray of light travels from glass (n=1.5) to air (n=1).

    For which angle of incidence will the ray just graze the surface (total internal reflection limit)?
    A 90° Correct Answer Incorrect Answer
    B 60° Correct Answer Incorrect Answer
    C 41.8° Correct Answer Incorrect Answer
    D 45° Correct Answer Incorrect Answer

    Solution

    The critical angle θC  for total internal reflection is: θC = sin-1 (n₂/n₁) = sin-1 (1/1.5) = sin-1 (0.666….) ≈ 41.8° At this angle, the refracted ray grazes the interface. Hence, the correct answer is 41.8°.

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