NCERT Book Class 8 Science Chapter 13 Light

LIGHT

T
he world is largely known through comb and close all its openings
the senses. The sense of sight except one in the middle. You can
is one of the most important use a strip of black paper for
senses. Through it we see mountains, this purpose. Hold the comb
rivers, trees, plants, chairs, people and perpendicular to the sheet of paper.
so many other things around us. We also
Throw light from a torch through
see clouds, rainbows and birds flying
the opening of the comb from one
in the sky. At night we see the moon
side (Fig. 13.1). With slight
and the stars. You are able to see the
adjustment of the torch and the
words and sentences printed on this
page. How is seeing made possible? comb you will see a ray of light along
the paper on the other side of the
13.1 What makes Things comb. Keep the comb and the torch
steady. Place a strip of plane mirror
Visible
in the path of the light ray
Have you ever thought how we see (Fig. 13.1). What do you observe?
various objects? You may say that eyes
see the objects. But, can you see an
object in the dark? It means that eyes
alone cannot see any object. It is only
when light from an object enters our
eyes that we see the object. The light
may have been emitted by the object, or
may have been reflected by it.
You learnt in Class VII that a polished
or a shiny surface can act as a mirror. A
mirror changes the direction of light
that falls on it. Can you tell in which
direction the light falling on a surface Fig. 13.1 : Arrangement for showing reflection
will be reflected? Let us find out.
After striking the mirror, the ray of
13.2 Laws of Reflection light is reflected in another direction.
Activity 13.1 The light ray, which strikes any surface,
is called the incident ray. The ray that
Fix a white sheet of paper on a comes back from the surface after
drawing board or a table. Take a reflection is known as the reflected ray.