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Question

AB and CD are two slabs. The medium between the slabs has refractive index 2. Find the minimum angle of incidence (in degrees) at Q so that the ray is totally reflected by both the slabs.
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Solution

Let the minimum angle be α
For first surface to completely reflect, 2Sinα2Sin90 => sinα1/2
=>α45

For second surface to completely reflect, 2Sinα3Sin90 => sinα3/2
=>

So satisfies both condition

Answer. Minimum angle of incidence so as to totally reflect from both surface is α=60



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