Explain about lenses

Lens are made from spherical transparent material as shown . Hence they are called spherical lenses.

Phenomenon of refraction of light is exploited to use the spherical lenses as light converging or

light diverging device depends on the type of lens.

 

we know that when light ray incident on a face of prism and making angle of incidence < 90° ,

it is getting refracted and light ray bend towards base of prism .

 

we know that when light ray incident on a face of glass slab ,

only lateral displacement takes place and emergent ray is parallel to incident ray .

This lateral displacement is prportional to thickness of glass slab.

 

As shown in figure,  a converging lens or convex lens is made up of two prisms at top and bottom

and in between a parallel slab. Hence light rays are getting converged as shown in figure for

converging or convex lens.

 

As shown in figure,  a diverging lens or concave lens is made up of two inverted prisms at top

and bottom and in between a parallel slab. Hence light rays are getting diverged as shown in figure

for diverging or concave lens.