A ray of light incident on an equilateral triangular glass prism of `mu = sqrt(3)` moves parallel to the base of the prism inside it. What is the angle of incidence for this ray ?

Explanation

When refracted ray is parallel to the base of the prism, deviation is minimum.
`:. r = A//2 = 60//2 = 30^@`
From `mu = (sin i)/(sin r)`
`sin i= mu sin r = sqrt(3) sin 30^@ =m sqrt(3)//2`
`:. i= 60^@`.