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A ray of light travelling in a transparent medium of refractive index μ, falls on a surface separating the medium from air at an angle of incidence of 45°. For which of the following value of μ the ray can undergo total internal reflection?

1. μ = 1.33
2. μ = 1.40
3. μ = 1.50
4. μ = 1.25

Correct answer: μ = 1.50

Solution

Total internal reflection occurs when the angle of incidence is greater than the critical angle. The critical angle is given by sin⁡C = 1/μ. For μ = 1.50, sin⁡C = 1/1.50 = 0.6667, so C ≈ 41.8°. Since the angle of incidence (45°) is greater than the critical angle, total internal reflection will occur.

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