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A light ray is incident perpendicular to one face of a 90° prism and is totally internally reflected at the glass-air interface. If the angle of reflection is 45°, we conclude that the refractive index n

Asked in JEE Main 2004 · Total internal reflection and optical fibres

• (1) n < 1/(√2)
• (2) n > √2
• (3) n > 1/(√2)
• (4) n < √2

Step-by-step solution

Why the other options are wrong

• (1) Writes sin C = n instead of 1/n, and also reverses the inequality.
• (3) Writes sin C = n instead of 1/n.
• (4) Reverses the condition: TIR needs the incidence angle to exceed C, i.e. C < 45°.

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