Given:
Refractive index of diamond, n1=2.42
Refractive index of glass,n2=1.5
Let the critical angle for the diamond glass interface be c.
Using the formula of critical angle,
sin c=n2n1
sin c≈0.6
The value of sine of critical angle is about 0.6 for the glass-diamond interface. The corresponding critical angle (c) comes out to be about 38∘.