Question

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

Answer 1

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°

Answer 2

Given:

The refractive index of glass with respect to air = 2 / 1

To find:

The critical angle (ic) of the glass-air interface

Solution:

The critical angle for an interface is the angle of incidence at which the incident ray when enters the rarer medium gets refracted and the refracted ray grazes along with the interface.

Using Snells's law at the interface,

μ1 sin i = μ2 sin r

When i = ic, the refracted ray grazes along with the interface, angle of refraction (r) = 90°

Hence,

sin ic = μ2 X sin 90 / μ1

or ic = sin⁻¹ 1/2

or ic = 30°

Hence, the critical angle of the glass-air interface is 30°.