Q. The speed of light in media M₁ and M₂ is 1.5 × 10⁸ m/s and 2.0 × 10⁸ m/s respectively. A ray of light enters from medium M₁ to M₂ at an incidence angle i. If the ray suffers total internal reflection, the value of i is
A) Equal to sin⁻¹(2/3)
B) Equal to or less than sin⁻¹(3/5)
C) Equal to or greater than sin⁻¹(3/4)
D) Less than sin⁻¹(2/3)
Explanation
[Solution from source] Refractive indices are μ₁ = c/v₁ = 2 and μ₂ = c/v₂ = 1.5. The critical angle satisfies sin C = μ₂/μ₁ = 3/4, so total internal reflection needs i equal to or greater than sin⁻¹(3/4). The value sin⁻¹(2/3) is obtained by wrongly using 1/μ₁ ratios; TIR never occurs for angles smaller than the critical angle. Answer (3).
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.