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A light wave travelling linearly in a medium of dielectric constant 4, incidents on the horizontal interface separating medium with air. The angle of incidence for which the total intensity of incident wave will be reflected back into the same medium will be
(Given: relative permeability of medium μᵣ=1)

Asked in JEE Main 25th June 1st Shift 2022 · Total internal reflection and optical fibres

• (1) 10°
• (2) 20°
• (3) 30°
• (4) 60°

Step-by-step solution

Why the other options are wrong

• (1) Below the critical angle, so part of the light refracts.
• (2) Below the critical angle, so part of the light refracts.
• (3) This is exactly the critical angle; TIR needs incidence greater than 30°.

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