Chapter: 10th Science : Chapter 2 : Optics
Lenses
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.
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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