CBSE Class 10 Answered

Hi dear,
When light passes through glass, it encounter two surfaces, one is the entry side and the other exit side. A light ray is refracted(bent) when it passes from one medium to another, thereby changing its speed.If the two interface surfaces are parallel to each other, all of the bending ( or dispersion)that takes place at the first interface is exactly reversed or counter effected at the other end, undoing the effect of first interface.
But, still the emerging ray is slightly displaced from the incoming ray, travels in the same direction as the incoming ray and all wave-lengths that got separated at the first interface now recombined.

Hope this helped.

Regards.

Topperearning.com