First slide

Total internal reflection - Ray optics and optical instruments

Question

The velocity of light in a medium is half its velocity in air. If ray of light emerges from such a medium into air, the angle of incidence, at which it will be totally internally reflected, is

Moderate

A

15°
B

30°
C

45°
D

60°

Solution

$μ = \frac{c}{v} \Rightarrow μ = \frac{c}{c / 2} = 2 also for total internal reflection$
$i > c \Rightarrow sini \geq sinc \Rightarrow sini \geq \frac{1}{μ} Hence i \geq \sin^{- 1} (\frac{1}{μ}) or i \geq 30^{\circ}$

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