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The speed of light in media 'A' and 'B' are 2.0×10¹⁰ cm/s and 1.5×10¹⁰ cm/s respectively. A ray of light enters from the medium B to A at an incident angle 'θ'. If the ray suffers total internal reflection, then

Asked in JEE Main 29th June 2nd Shift 2022 · Total internal reflection and optical fibres

• (1) θ=sin⁻¹(3/4)
• (2) θ>sin⁻¹(2/3)
• (3) θ<sin⁻¹(3/4)
• (4) θ>sin⁻¹(3/4)

Step-by-step solution

Why the other options are wrong

• (1) At exactly the critical angle the ray grazes the surface; TIR needs a larger angle.
• (2) Uses 2/3 from a wrong speed ratio.
• (3) Reverses the inequality; smaller angles let light refract.

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