Question

A beam of light is traveling inside a solid glass cube that has index of refraction 1.68. It strikes the surface of the cube from the inside.

Part A

If the cube is in air, at what minimum angle with the normal inside the glass will this light not enter the air at this surface?

Part B

What would be the minimum angle in part A if the cube was immersed in water?

Answer 1

here,

the index of refraction of cube , n = 1.68

a)

refractive index of air , n' = 1

minimum angle with the normal inside the glass will this light not enter the air at this surface is the critical angle

the minimum angle with the normal inside the glass , theta = arcsin(n'/n)

theta = arcsin( 1/1.68)

theta = 36.53 degree

the minimum angle with the normal inside the glass will this light not enter the air at this surface is 36.53 degree

B)

refractive index of water , n' = 1.33

minimum angle with the normal inside the glass will this light not enter the air at this surface is the critical angle

the minimum angle with the normal inside the glass , theta = arcsin(n'/n)

theta = arcsin( 1.33/1.68)

theta = 52.34 degree

the minimum angle with the normal inside the glass will this light not enter the air at this surface is 52.34 degree