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In the above example, find the angle of ...

In the above example, find the angle of incidence at face `AB`, so that emergent ray grazes along the face `AC'`.

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In Fig., refracted ray `LM` suffers total internal reflection on face `AC` and grazes along the face `AC`.

`:. angleLMN' = C`, critical angle
As `sin C = (1)/(mu) = (1)/(sqrt(2)) :. C = 45^(@)`
`:. angleAML = 90^(@) - 45^(@) = 45^(@)`
`r = 90^(@) - 75^(@) =15^(@)`
From `mu = (sin i)/(sin r)`
`sin i = mu sin r = sqrt(2) sin 15^(@)`
`= 1.414 xx 0.2588 = 0.3659`
`i = sin^(-1)(0.3659) = 21.46^(@)`
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