Page 150 - NCERT Science Class 10 English Medium

1 − 5.0 + 3.0 − 2.0
or, = = or, v = – 37.5 cm
v 75.0 75.0
The screen should be placed at 37.5 cm in front of the mirror. The
image is real.
h ' v
Also, magnification, m = = −
h u
v h ( 37.5cm) ( 4.0cm)
+
−
or, h′ = – = −
u ( 25.0 cm)
−
Height of the image, h′ = – 6.0 cm
The image is inverted and enlarged.

Q U E S T I O N S

1. Find the focal length of a convex mirror whose radius of curvature is
32 cm.
2. A concave mirror produces three times magnified (enlarged) real image ?
of an object placed at 10 cm in front of it. Where is the image located?

9.3 REFRACTION OF LIGHTREFRACTION OF LIGHT
9.3 REFRACTION OF LIGHT
OF
LIGHT
9.3
9.3 REFRACTION
9.3 REFRACTION OF LIGHT
Light seems to travel along straight-line paths in a transparent medium.
What happens when light enters from one transparent medium to
another? Does it still move along a straight-line path or change its
direction? We shall recall some of our day-to-day experiences.
You might have observed that the bottom of a tank or a pond
containing water appears to be raised. Similarly, when a thick glass slab
is placed over some printed matter, the letters appear raised when viewed
through the glass slab. Why does it happen? Have you seen a pencil
partly immersed in water in a glass tumbler? It appears to be displaced
at the interface of air and water. You might have observed that a lemon
kept in water in a glass tumbler appears to be bigger than its actual
size, when viewed from the sides. How can you account for such
experiences?
Let us consider the case of the apparent displacement of a pencil,
partly immersed in water. The light reaching you from the portion of the
pencil inside water seems to come from a different direction, compared
to the part above water. This makes the pencil appear to be displaced at
the interface. For similar reasons, the letters appear to be raised, when
seen through a glass slab placed over it.
Does a pencil appear to be displaced to the same extent, if instead of
water, we use liquids like kerosene or turpentine? Will the letters appear
to rise to the same height if we replace a glass slab with a transparent
plastic slab? You will find that the extent of the effect is different for
different pair of media. These observations indicate that light does not

Light – Reflection and Refraction 145

2024-25