Lenses
What is a Lens?
LENSES
A lens is an optically transparent medium bounded by two spherical refracting surfaces or one plane and one spherical surface.
Lens is basically classified into two types.
Primary Types of Lenses
They are:
- (i) Convex Lens
- (ii) Concave Lens
(i) Convex or bi-convex lens:
It is a lens bounded by two spherical surfaces such that it is thicker at the centre than at the edges. A beam of light passing through it, is converged to a point. So, a convex lens is also called as converging lens.
(ii) Concave or bi-concave Lens:
It is a lens bounded by two spherical surfaces such that it is thinner at the centre than at the edges. A parallel beam of light passing through it, is diverged or spread out. So, a concave lens is also called as diverging lens.
Other types of Lenses
Plano-convex lens:
If one of the faces of a bi-convex lens is plane, it is known as a plano-convex lens.
Plano-concave lens:
If one of the faces of a bi-concave lens is plane, it is known as a plano-concave lens.
All these lenses are shown in Figure 2.2 given below:
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10th Science : Chapter 2 : Optics : Lenses