Write a short note on lens and its types.

Explanation

A lens is a transparent medium bound by two surfaces. Depending on the nature of two surfaces there are different types of lenses.
i. Convex lens: The lens which has two spherical surfaces puffed up outwards is called convex lens or double convex lens (biconvex). This lens is thicker at the centre than at the edges.
ii. Concave lens: The lens with both spherical surfaces on the inside is called concave lens or double concave lens (biconcave). This lens is thinner at the centre than at the edges.
iii. Other than these main two types, lenses like piano-convex, piano-concave, positive meniscus, negative meniscus lenses are also fabricated.