Question

Describe giving reason the path a ray of light incident on a glass slab till it emerge to the slab

Answer 1

When a light ray incident on glass slab at any angle other than normal then it passes from air to glass. As light ray travels from rarer medium to denser medium it bends towards the normal. Inside glass slab refracted light ray travel straight path. Again at the boundary of glass slab, when light ray travels from glass to water that is from denser to rarer medium, light ray bends away from normal and travel as emergent ray.

Answer 2

In a glass slab the opposite faces are parallel so the angle of refraction of air glass interface becomes the angle of incidence for glass-air interface.

By the principal of reversibility the emergent ray bends such that angle of incidence becomes equal to angle of emergence.

Let  denotes refractive index of glass with respect to air i.e first interface(air-glass) where the incident ray goes.

and  be refractive index of second interface i.e glass-air interface from where the ray emerges out.

then  =       ...(i)

and  =        ....(ii)

=  =       ...(iii)

From (iii)

x  = 1

Since  =  (parallel lines concept alternate interior angles)

sin  = sin

So  =

Angle of incidence and angle of emergence while coming out are equal and hence there is just a shift but the lines are parallel.