A ray of light passing from air through an equilateral glass prism undergoes minimum deviation when the angle of incidence is 3/4th of the angle of prism. Calculate the speed of light in the prism.

Here, Angle of prism, A = 60°
Angle of incidence, i = (3/4) × 60
i + e = A + δ
e is emergence angle
where δ is deviation angle
At minimum deviation δ = δmin
i = e
2i = A + δmin
2 × 45 = 60 + δmin
δmin = 30
By prism law, μ = sin((A + δmin)/2) / sin(A/2)
μ = sin((60 + 30)/2) / sin(60/2)
= sin(45) / sin(30)
= (1/√2) / (1/2)
= 2/√2 = √2 = 1.41
Let v be velocity of light in prism
v = c/μ
= 3 × 10^8 / 1.41
= 2 × 10^8 m/s