Firstly extend the normals such that they meet inside the prism. Let the angle between them be A. The other two angles of this triangle are r1 and r2. Since the refractive index has increased, the ray will bend slightly more towards the normal i.e. r1 decreases to say r1’ and the ray will hit the other edge slightly lower down. Form a new triangle. The angle A remains the same as it is the angle between the two normals . Since r1’ < r1, r2’ > r2 because
r1 + r2 + A = r1’ + r2’ + A = 180.
We have μ’ > μ
Now, R.I. μ’ = sin 30 / sin r1’ = sin e / sin r2’.
Since r2’ > r2, Sin e has to increase to get the same μ’, or e > 60.
Extend this ray back to find the new angle of deviation.
It will be found to have increased.
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