According to Snell's when light passes from one medium to another medium its velocity changes due to which light refracts in lens.
The term 'light' sometimes refers to electromagnetic radiation of any wavelength, whether visible or not. In this sense, gamma rays, X-rays, microwaves and radio waves are also light. ... However, the energy imparted by the waves is absorbed at single locations the way particles are absorbed.Each light ray entering a converging (convex) lens refracts inwards as it enters the lens and inwards again as it leaves. These refractions cause parallel light rays to spread out, travelling directly away from an imaginary focal point.
Refraction is an effect that occurs when a light wave, incident at an angle away from the normal, passes a boundary from one medium into another in which there is a change in velocity of the light. Light is refracted when it crosses the interface from air into glass in which it moves more slowly.A traditional lens is essentially a curved piece of glass that bends light through a process known as "refraction".
The bending of a ray of light also occurs when light passes into and out of a glass lens. However, because of the curved surfaces of the lens, the bending causes the light rays in a beam either to come together (converge, picture on left-hand side) or to spread out (diverge, picture on right-hand side).Glass is a perfect everyday example of light refraction. Looking through a glass jar will make an object look smaller and slightly lifted. If a slab of glass is placed over a document or piece of paper, then the words will look closer to the surface because of the different angle the light is bending.