A ray of light is transferred from one medium which is transparent to the another medium by changing the direction. In different transparent media velocity of light is different. The law of refraction is given as incident ray and refracted ray are normal to the surface separating two media all lie in the same plane.

The ratio of sine of angle of incidence to the sine of angle of refraction is constant.Refraction through Glass Slab:Refraction through glass slab is given here,Draw a line which appears in raised position on a paper and it is placed on the glass slab is placed by shiting up.Similarly bottom of the swimming pool which appeared to be raised. Light is refracted by the glass slab is very much responsible for this fact.

The refraction is shown here,refractionAs given in the above figure a ray of light AB incident at a point B on surface PQ at an angle `theta`1 at a point B ray AB is refracted and BC is a refracted ray. This refracted ray is incident at a point C on a surface at an angle `theta`3 and emergent ray CD emerges from rectangular slab through glass slab.At the surface PQ `eta` =1.Using the equation `eta`1 sin`theta`1 = `eta`2sin`theta`2,`eta`2sin`theta`2 = `eta`1 sin`theta`1 = sin `theta`1For a second surface RS parallel to PQ.`eta`2sin`theta`3 = `eta`3sin`theta`4,`eta`2sin`theta`2 = `eta`3sin`theta`4 ( `theta`2 = `theta`3)`eta`2sin`theta`2 = sin `theta`4 ( `eta`3 =1)`:.` sin `theta`1 = sin `theta`4`theta`1 = `theta`4.It is clear that the direction of emergent ray CD is parallel to incident ray ABEF but because of the refraction emergent ray displaced by perpendicular distance CE.

This kind of displacement is known as lateral shift. The lateral shift is proportional to perpendicular distance between two refracting surfaces. From the above given figure CE is referred as the lateral shift.Example for Refraction through Glass SlabThe position of the slab is marked bu placing the slab in the position. Fix two pins on one side of the slab and observe and from other side of the glass slab. Arrange the other two pins in such a way that all four pins appear to be in a straight line. Trace the path of the ray and prove that the lateral shift is proportional to perpendicular distance between the two refracting surfaces by repeating the activity through the another rectangular glass slab.