NCERT Book Class 10 Science Chapter 9 Light – Reflection and Refraction

CHAPTER 9
Light – Reflection and
Refraction

W e see a variety of objects in the world around us. However, we are
unable to see anything in a dark room. On lighting up the room,
things become visible. What makes things visible? During the day, the
sunlight helps us to see objects. An object reflects light that falls on it.
This reflected light, when received by our eyes, enables us to see things.
We are able to see through a transparent medium as light is transmitted
through it. There are a number of common wonderful phenomena
associated with light such as image formation by mirrors, the twinkling
of stars, the beautiful colours of a rainbow, bending of light by a medium
and so on. A study of the properties of light helps us to explore them.
By observing the common optical phenomena around us, we may
conclude that light seems to travel in straight lines. The fact that a small
source of light casts a sharp shadow of an opaque object points to this
straight-line path of light, usually indicated as a ray of light.
More to Know!

If an opaque object on the path of light becomes very small, light has a tendency to
bend around it and not walk in a straight line – an effect known as the diffraction of
light. Then the straight-line treatment of optics using rays fails. To explain phenomena
such as diffraction, light is thought of as a wave, the details of which you will study
in higher classes. Again, at the beginning of the 20th century, it became known that
the wave theory of light often becomes inadequate for treatment of the interaction of
light with matter, and light often behaves somewhat like a stream of particles. This
confusion about the true nature of light continued for some years till a modern
quantum theory of light emerged in which light is neither a ‘wave’ nor a ‘particle’ –
the new theory reconciles the particle properties of light with the wave nature.

In this Chapter, we shall study the phenomena of reflection and
refraction of light using the straight-line propagation of light. These basic
concepts will help us in the study of some of the optical phenomena in
nature. We shall try to understand in this Chapter the reflection of light
by spherical mirrors and refraction of light and their application in real
life situations.

9.1 REFLECTION OF LIGHT
A highly polished surface, such as a mirror, reflects most of the light
falling on it. You are already familiar with the laws of reflection of light.

134 Science