Page 151 - Physics_Form_2

Nature and reflection of light

It is observed that, depending on the object position, an image formed by a concave
mirror can be virtual or real, enlarged or diminished, upright or inverted. The amount
by which the size of the object is enlarged or diminished is called magnification, and
is given by:
image size image distance
m= =
object size object distance
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Example 4.3
An object 20 cm high is placed 40 cm in front of a concave mirror of focal length
15 cm. Determine the position, nature, size and magnification of the image formed
using a ray diagram.

Solution
1. Choose a scale of 1 cm to represent 5 cm.

2. Draw the principal axis of the mirror and mark the focal point as shown in Figure
4.24 (a).
3. Draw the object position. Using the chosen scale, the object will be 4 cm high at
a distance of 8 cm from the mirror as shown in Figure 4.25 (b).

F
4 cm

O 3 cm
3 cm 8 cm

(a) (b)

Figure 4.25

4. Locate the position of the image by drawing rays from the object to the mirror
and the reflected rays as follows:

(a) From the head of the object, draw ray 1 parallel to the principal axis. This
ray will be reflected through the focal point.
(b) From the head of the object, draw ray 2 through the focal point. This ray will
be reflected parallel to the principal axis.
(c) At the point of intersection of the two reflected rays, construct the image as
shown in Figure 4.26.

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Physics Form 2 Final.indd 145 25/10/2025 10:27