Question

the refractive index of Glass with respect to air is 2 then the critical angle of Glass air interface is

Answer 1

refractive index of Glass with respect to air is 2

Let the critical angle = c

We know that
$\mu = \frac{1}{ \sin(c) } \\ \\ 2 = \frac{1}{ \sin(c) } \\ \\ \sin(c) = \frac{1}{2} \\ \\ \sin(c) = \sin(30) \\ \\ c = {30}^{o}$

critical angle of glass air interface is 30°

Answer 2

For critical angle , the raay will go from glass to air.

By snell's law  

µgsinc = µasin90

or  

sinc=µa.1/µg

according to question µg/µa =2

then  

sinc = 1/2

c=sin^-1(1/2)

angle c =30°