Lenses
Optical devices such as the camera of mobile, DSLR, human eye- have lenses. The lens is made of transparent materials and the lens refracts the incident light. Depending on the type of lens, the rays can converge or diverge from the lens. In this unit, we will learn about only two types of lenses:
convex lens and concave lens.
What is the lens?
A transparent material bound by at least one curved surface is called the lens.
Convex and concave both the lenses have two curved surfaces.
Focus point and focal length of Convex lens
The rays of light travelling parallel to the principal axis of a convex lens, after refraction, converges towards the principal axis.
The point where the rays meet is called a focus point. The distance between focus point and the optical centre of a convex lens is called as its focal length.
Note: In lenses, all the distances are measured from the optical centre of the lens
Focus point and focal length of a Concave lens
The rays of light traveling parallel to the principal axis of a concave lens, after refraction, diverge and appear to meet on the principal axis of the lens. The point where rays meet is called a focus point.
The distance between focus point and the optical centre of a lens is its focal length.
