Refraction through a rectangular Glass slab :

A ray of light AO travelling in air is incident on a rectangular Glass slab PQRS at point O.

The light emerges from a parallel-sided glass slab in a direction parallel with that in which it enters the glass slab.

The perpendicular distance between the original path of incident Ray and the emergent ray coming out of the glass slab is called Lateral displacement. 

The angle which the emergent ray makes with the normal is called the angle of emergence.

Factors affecting lateral shift are :

1. Angle of incidence.
2. Thickness of the Glass slab.
3. Refractive index of the glass slab.
4. Wavelength of the incident light.
5. Pair of medium.

Effects of Refraction of light :

1. A stick ( on Pencil ) held obliquely and partly immersed in water appear to be bent at the water surface.
2. An object placed under water appears to be raised.
3. A pool of water appears to be less deep to raised.
4. When a thick glass slab is placed over some printed matter , the letters appear raised when viewed from the top.
5. A lemon kept in water in a glass tumbler appears to be bigger than its actual size , when viewed from the sides.
6. The stars appears to twinkle on a clear night.