Page 143 - NCERT Science Class 10 English Medium

You will see in the above Activity that the nature, position and size of
the image formed by a concave mirror depends on the position of the
object in relation to points P, F and C. The image formed is real for some
positions of the object. It is found to be a virtual image for a certain other
position. The image is either magnified, reduced or has the same size,
depending on the position of the object. A summary of these observations
is given for your reference in Table 9.1.
Table 9.1 Image formation by a concave mirror for different positions of the object

Position of the Position of the Size of the Nature of the
object image image image

At infinity At the focus F Highly diminished, Real and inverted
point-sized
Beyond C Between F and C Diminished Real and inverted

At C At C Same size Real and inverted
Between C and F Beyond C Enlarged Real and inverted
At F At infinity Highly enlarged Real and inverted

Between P and F Behind the mirror Enlarged Virtual and erect

9.2.2 Representation of Images Formed by Spherical
Mirrors Using Ray Diagrams

We can also study the formation of images by spherical mirrors by
drawing ray diagrams. Consider an extended object, of finite size, placed
in front of a spherical mirror. Each small portion of the extended object
acts like a point source. An infinite number of rays originate from each
of these points. To construct the ray diagrams, in order to locate the
image of an object, an arbitrarily large number of rays emanating from a
point could be considered. However, it is more convenient to consider
only two rays, for the sake of clarity of the ray diagram. These rays are
so chosen that it is easy to know their directions after reflection from the
mirror.
The intersection of at least two reflected rays give the position of image
of the point object. Any two of the following rays can be considered for
locating the image.

(i) A ray parallel to the principal
axis, after reflection, will pass
through the principal focus
in case of a concave mirror
or appear to diverge from
the principal focus in
case of a convex mirror.
This is illustrated in Fig.9.3
(a) (b)
Figure 9.3
Figure 9.39.3
Figure
Figure 9.3 (a) and (b).
Figure 9.3
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