We know that , lens is the combination of large number of prism. In convex lens upper prism has base downward where as lower prism has base upward as shown in the figure. The middle part of the lens acts as thin glass slab. The light ray's incident on prism refracts towards its base but the light ray passing from center does not bend. Hence, it refracts the light as in figure below:
A convex lens causes parallel light rays to meet at a focal point. A concave lens causes parallel light rays to spread out. The focal point is the point at which parallel light rays meet after being reflected or refracted. Distort means to change the shape of something by twisting or moving the parts around.A converging lens will cause the light rays to bend to a specific focal point.
Lenses serve to refract light at each boundary. As a ray of light enters a lens, it is refracted; and as the same ray of light exits the lens, it is refracted again.The amount of bending depends on two things: Change in speed – if a substance causes the light to speed up or slow down more, it will refract (bend) more. Angle of the incident ray – if the light is entering the substance at a greater angle, the amount of refraction will also be more noticeable.