Page 140 - NCERT Science Class 10 English Medium

Let us recall these laws –
(i) The angle of incidence is equal to the angle of reflection, and
(ii) The incident ray, the normal to the mirror at the point of incidence
and the reflected ray, all lie in the same plane.
These laws of reflection are applicable to all types of reflecting surfaces
including spherical surfaces. You are familiar with the formation of image
by a plane mirror. What are the properties of the image? Image formed
by a plane mirror is always virtual and erect. The size of the image is
equal to that of the object. The image formed is as far behind the mirror
as the object is in front of it. Further, the image is laterally inverted.
How would the images be when the reflecting surfaces are curved? Let
us explore.

Activity
Activity 9.19.1
Activity 9.1
9.1
Activity 9.1
Activity
n Take a large shining spoon. Try to view your face in its curved
surface.
n Do you get the image? Is it smaller or larger?
n Move the spoon slowly away from your face. Observe the image.
How does it change?
n Reverse the spoon and repeat the Activity. How does the image
look like now?
n Compare the characteristics of the image on the two surfaces.

The curved surface of a shining spoon could be considered as a curved
mirror. The most commonly used type of curved mirror is the spherical
mirror. The reflecting surface of such mirrors can be considered to form
a part of the surface of a sphere. Such mirrors, whose reflecting surfaces
are spherical, are called spherical mirrors. We shall now study about
spherical mirrors in some detail.

9.2
9.2
9.2 SPHERICAL MIRRORS
9.2 SPHERICSPHERICAL MIRRORSAL MIRRORS
SPHERIC
9.2 SPHERICAL MIRRORSAL MIRRORS
The reflecting surface of a spherical mirror may be curved inwards or
outwards. A spherical mirror, whose reflecting surface is curved inwards,
that is, faces towards the centre of the sphere, is called a concave mirror.
A spherical mirror whose reflecting surface is curved outwards, is called
a convex mirror. The schematic representation of these mirrors is shown
in Fig. 9.1. You may note in these diagrams that the back
of the mirror is shaded.
You may now understand that the surface of the spoon
curved inwards can be approximated to a concave mirror
and the surface of the spoon bulged outwards can be
approximated to a convex mirror.
Before we move further on spherical mirrors, we need to
recognise and understand the meaning of a few terms. These
terms are commonly used in discussions about spherical (a) Concave mirror (b) Convex mirror
mirrors. The centre of the reflecting surface of a spherical Figure 9.1
Figure 9.1
Figure
Figure
9.1
Figure 9.19.1
mirror is a point called the pole. It lies on the surface of the Schematic representation of spherical
mirror. The pole is usually represented by the letter P. mirrors; the shaded side is non-reflecting.
Light – Reflection and Refraction 135

2024-25