By Snell’s law, in case of prism,
![](https://www.sarthaks.com/?qa=blob&qa_blobid=9237204828835996997)
For equilateral prism, A = 60°
Also, A = r1 + r2
∴ r2 = A – r1 = 60° – 23°39′ = 36°21′
Applying snell’s law on the second surface of
![](https://www.sarthaks.com/?qa=blob&qa_blobid=6607552876848946717)
= 62°44′
≈ 63°
For any prism,
i + e = A + δ
∴ δ = (i + e) – A
= (37 + 63) – 60
= 40°
For an emergent ray to just emerge, the angle r’2 acts as a critical angle.
![](https://www.sarthaks.com/?qa=blob&qa_blobid=16156100775688718850)
As, A = r’1 + r’2 and i to be kept the same.
![](https://www.sarthaks.com/?qa=blob&qa_blobid=417879652016244665)