NCERT Textbook: Light

# NCERT Textbook: Light | Science & Technology for UPSC CSE PDF Download

``` Page 1

LIGHT
LIGHT
T
he world is largely known through
the senses. The sense of sight
is one of the most important
senses. Through it we see mountains,
rivers, trees, plants, chairs, people and
so many other things around us. We also
see clouds, rainbows and birds flying
in the sky. At night we see the moon
and the stars. You are able to see the
words and sentences printed on this
page. How is seeing made possible?
13.1 What makes Things
Visible
Have you ever thought how we see
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
will be reflected? Let us find out.
13.2 Laws of Reflection
Activity 13.1
Fix a white sheet of paper on a
drawing board or a table. Take a
comb and close all its openings
except one in the middle. You can
use a strip of black paper for
this purpose. Hold the comb
perpendicular to the sheet of paper.
Throw light from a torch through
the opening of the comb from one
side (Fig. 13.1). With slight
adjustment of the torch and the
comb you will see a ray of light along
the paper on the other side of the
comb. Keep the comb and the torch
steady. Place a strip of plane mirror
in the path of the light ray
(Fig. 13.1). What do you observe?
After striking the mirror, the ray of
light is reflected in another direction.
The light ray, which strikes any surface,
is called the incident ray. The ray that
comes back from the surface after
reflection is known as the reflected ray.
Fig. 13.1 : Arrangement for showing reflection
Rationalised-2023-24
Page 2

LIGHT
LIGHT
T
he world is largely known through
the senses. The sense of sight
is one of the most important
senses. Through it we see mountains,
rivers, trees, plants, chairs, people and
so many other things around us. We also
see clouds, rainbows and birds flying
in the sky. At night we see the moon
and the stars. You are able to see the
words and sentences printed on this
page. How is seeing made possible?
13.1 What makes Things
Visible
Have you ever thought how we see
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
will be reflected? Let us find out.
13.2 Laws of Reflection
Activity 13.1
Fix a white sheet of paper on a
drawing board or a table. Take a
comb and close all its openings
except one in the middle. You can
use a strip of black paper for
this purpose. Hold the comb
perpendicular to the sheet of paper.
Throw light from a torch through
the opening of the comb from one
side (Fig. 13.1). With slight
adjustment of the torch and the
comb you will see a ray of light along
the paper on the other side of the
comb. Keep the comb and the torch
steady. Place a strip of plane mirror
in the path of the light ray
(Fig. 13.1). What do you observe?
After striking the mirror, the ray of
light is reflected in another direction.
The light ray, which strikes any surface,
is called the incident ray. The ray that
comes back from the surface after
reflection is known as the reflected ray.
Fig. 13.1 : Arrangement for showing reflection
Rationalised-2023-24
SCIENCE 166
A ray of light is an idealisation. In
reality, we have a narrow beam of
light which is made up of several
rays. For simplicity, we use the term
ray for a narrow beam of light.
Draw lines showing the position of
the plane mirror, the incident ray and
the reflected ray on the paper with the
help of your friends. Remove the mirror
and the comb. Draw a line making an
angle of 90º to the line representing the
mirror at the point where the incident
ray strikes the mirror. This line is known
as the normal to the reflecting surface
at that point (Fig. 13.2). The angle
Table 13.1 :Angles of Incidence
and Reflection
S. Angle of Angle of
No. Incidence (? ? ? ? ?i) Reflection (? ? ? ? ?r)
1.
2.
3.
4.
5.
Do you see any relation between the
angle of incidence and the angle of
reflection. Are they approximately equal?
If the experiment is carried out carefully,
it is seen that the angle of incidence is
always equal to the angle of reflection.
This is one of the laws of reflection.
Let us perform another activity on
reflection.
What would happen if I
threw the light on the
mirror along the normal.
Activity 13.2
Perform Activity 13.1 again. This
time use a sheet of stiff paper or a
chart paper. Let the sheet project a
little beyond the edge of the Table
(Fig. 13.4). Cut the projecting
portion of the sheet in the middle.
Look at the reflected ray. Make sure
that the reflected ray extends to the
projected portion of the paper. Bend
that part of the projected portion on
which the reflected ray falls. Can
you still see the reflected ray? Bring
the paper back to the original
Fig. 13.2 : Drawing the normal
Fig. 13.3 : Angle of incidence and angle of
reflection
Reflected
ray
Normal
Incident
ray
between the normal and incident ray is
called the angle of incidence (? ? ? ? ?i). The
angle between the normal and the
reflected ray is known as the angle of
reflection (? ? ? ? ?r) (Fig. 13.3). Measure the
angle of incidence and the angle of
reflection. Repeat the activity several
times by changing the  angle of
incidence. Enter the data  in Table 13.1.
Rationalised-2023-24
Page 3

LIGHT
LIGHT
T
he world is largely known through
the senses. The sense of sight
is one of the most important
senses. Through it we see mountains,
rivers, trees, plants, chairs, people and
so many other things around us. We also
see clouds, rainbows and birds flying
in the sky. At night we see the moon
and the stars. You are able to see the
words and sentences printed on this
page. How is seeing made possible?
13.1 What makes Things
Visible
Have you ever thought how we see
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
will be reflected? Let us find out.
13.2 Laws of Reflection
Activity 13.1
Fix a white sheet of paper on a
drawing board or a table. Take a
comb and close all its openings
except one in the middle. You can
use a strip of black paper for
this purpose. Hold the comb
perpendicular to the sheet of paper.
Throw light from a torch through
the opening of the comb from one
side (Fig. 13.1). With slight
adjustment of the torch and the
comb you will see a ray of light along
the paper on the other side of the
comb. Keep the comb and the torch
steady. Place a strip of plane mirror
in the path of the light ray
(Fig. 13.1). What do you observe?
After striking the mirror, the ray of
light is reflected in another direction.
The light ray, which strikes any surface,
is called the incident ray. The ray that
comes back from the surface after
reflection is known as the reflected ray.
Fig. 13.1 : Arrangement for showing reflection
Rationalised-2023-24
SCIENCE 166
A ray of light is an idealisation. In
reality, we have a narrow beam of
light which is made up of several
rays. For simplicity, we use the term
ray for a narrow beam of light.
Draw lines showing the position of
the plane mirror, the incident ray and
the reflected ray on the paper with the
help of your friends. Remove the mirror
and the comb. Draw a line making an
angle of 90º to the line representing the
mirror at the point where the incident
ray strikes the mirror. This line is known
as the normal to the reflecting surface
at that point (Fig. 13.2). The angle
Table 13.1 :Angles of Incidence
and Reflection
S. Angle of Angle of
No. Incidence (? ? ? ? ?i) Reflection (? ? ? ? ?r)
1.
2.
3.
4.
5.
Do you see any relation between the
angle of incidence and the angle of
reflection. Are they approximately equal?
If the experiment is carried out carefully,
it is seen that the angle of incidence is
always equal to the angle of reflection.
This is one of the laws of reflection.
Let us perform another activity on
reflection.
What would happen if I
threw the light on the
mirror along the normal.
Activity 13.2
Perform Activity 13.1 again. This
time use a sheet of stiff paper or a
chart paper. Let the sheet project a
little beyond the edge of the Table
(Fig. 13.4). Cut the projecting
portion of the sheet in the middle.
Look at the reflected ray. Make sure
that the reflected ray extends to the
projected portion of the paper. Bend
that part of the projected portion on
which the reflected ray falls. Can
you still see the reflected ray? Bring
the paper back to the original
Fig. 13.2 : Drawing the normal
Fig. 13.3 : Angle of incidence and angle of
reflection
Reflected
ray
Normal
Incident
ray
between the normal and incident ray is
called the angle of incidence (? ? ? ? ?i). The
angle between the normal and the
reflected ray is known as the angle of
reflection (? ? ? ? ?r) (Fig. 13.3). Measure the
angle of incidence and the angle of
reflection. Repeat the activity several
times by changing the  angle of
incidence. Enter the data  in Table 13.1.
Rationalised-2023-24
LIGHT 167
position. Can you see the reflected
ray again? What do you infer?
with the Sun as the source of light
instead of a torch. You, too, can use the
Sun as the source of light.
These activities can also be performed
by making use of the Ray Streak
Apparatus (available in the kit
prepared by NCERT).
Boojho remembered that in Class VII,
he had studied some features of the
image of an object formed by a plane
mirror. Paheli asked him to recall
those features:
(i) Was the image erect or upside
down?
(ii) Was it of the same size as the
object?
(iii) Did the image appear at  the same
distance behind the mirror as the
object was in front of it?
(iv) Could it be obtained on a screen?
Let us understand a little more about
the formation of an image by a plane
mirror in the following way:
Activity 13.3
A source of light O is placed in front
of a plane mirror PQ. Two rays OA
and OC are incident on it (Fig. 13.5).
Can you find out the direction of
the reflected rays?
Draw normals to the surface of
the mirror PQ, at the points A and
C. Then draw the reflected rays at
the points A and C. How would you
draw these rays? Call the reflected
rays AB and CD, respectively.
Extend them further. Do they meet?
Extend them backwards. Do they
meet now? If they meet, mark this
point as I. For a viewer’s eye at E
(Fig. 13 .5), do the reflected rays
(b)
Fig. 13.4 (a), (b) : Incident ray, reflected ray
and the normal at the point
of incidence lie in the same
plane
When the whole sheet of paper is
spread on the table, it represents one
plane. The incident ray, the normal at
the point of incidence and the reflected
ray are all in this plane. When you bend
the paper you create a plane different
from the plane in which the incident
ray and the normal lie. Then you do not
see the reflected ray. What does it
indicate? It indicates that the incident
ray, the normal at the point of
incidence and the reflected ray all lie
in the same plane. This is another law
of reflection.
Paheli and Boojho performed the
above activities outside the classroom
(a)
Rationalised-2023-24
Page 4

LIGHT
LIGHT
T
he world is largely known through
the senses. The sense of sight
is one of the most important
senses. Through it we see mountains,
rivers, trees, plants, chairs, people and
so many other things around us. We also
see clouds, rainbows and birds flying
in the sky. At night we see the moon
and the stars. You are able to see the
words and sentences printed on this
page. How is seeing made possible?
13.1 What makes Things
Visible
Have you ever thought how we see
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
will be reflected? Let us find out.
13.2 Laws of Reflection
Activity 13.1
Fix a white sheet of paper on a
drawing board or a table. Take a
comb and close all its openings
except one in the middle. You can
use a strip of black paper for
this purpose. Hold the comb
perpendicular to the sheet of paper.
Throw light from a torch through
the opening of the comb from one
side (Fig. 13.1). With slight
adjustment of the torch and the
comb you will see a ray of light along
the paper on the other side of the
comb. Keep the comb and the torch
steady. Place a strip of plane mirror
in the path of the light ray
(Fig. 13.1). What do you observe?
After striking the mirror, the ray of
light is reflected in another direction.
The light ray, which strikes any surface,
is called the incident ray. The ray that
comes back from the surface after
reflection is known as the reflected ray.
Fig. 13.1 : Arrangement for showing reflection
Rationalised-2023-24
SCIENCE 166
A ray of light is an idealisation. In
reality, we have a narrow beam of
light which is made up of several
rays. For simplicity, we use the term
ray for a narrow beam of light.
Draw lines showing the position of
the plane mirror, the incident ray and
the reflected ray on the paper with the
help of your friends. Remove the mirror
and the comb. Draw a line making an
angle of 90º to the line representing the
mirror at the point where the incident
ray strikes the mirror. This line is known
as the normal to the reflecting surface
at that point (Fig. 13.2). The angle
Table 13.1 :Angles of Incidence
and Reflection
S. Angle of Angle of
No. Incidence (? ? ? ? ?i) Reflection (? ? ? ? ?r)
1.
2.
3.
4.
5.
Do you see any relation between the
angle of incidence and the angle of
reflection. Are they approximately equal?
If the experiment is carried out carefully,
it is seen that the angle of incidence is
always equal to the angle of reflection.
This is one of the laws of reflection.
Let us perform another activity on
reflection.
What would happen if I
threw the light on the
mirror along the normal.
Activity 13.2
Perform Activity 13.1 again. This
time use a sheet of stiff paper or a
chart paper. Let the sheet project a
little beyond the edge of the Table
(Fig. 13.4). Cut the projecting
portion of the sheet in the middle.
Look at the reflected ray. Make sure
that the reflected ray extends to the
projected portion of the paper. Bend
that part of the projected portion on
which the reflected ray falls. Can
you still see the reflected ray? Bring
the paper back to the original
Fig. 13.2 : Drawing the normal
Fig. 13.3 : Angle of incidence and angle of
reflection
Reflected
ray
Normal
Incident
ray
between the normal and incident ray is
called the angle of incidence (? ? ? ? ?i). The
angle between the normal and the
reflected ray is known as the angle of
reflection (? ? ? ? ?r) (Fig. 13.3). Measure the
angle of incidence and the angle of
reflection. Repeat the activity several
times by changing the  angle of
incidence. Enter the data  in Table 13.1.
Rationalised-2023-24
LIGHT 167
position. Can you see the reflected
ray again? What do you infer?
with the Sun as the source of light
instead of a torch. You, too, can use the
Sun as the source of light.
These activities can also be performed
by making use of the Ray Streak
Apparatus (available in the kit
prepared by NCERT).
Boojho remembered that in Class VII,
he had studied some features of the
image of an object formed by a plane
mirror. Paheli asked him to recall
those features:
(i) Was the image erect or upside
down?
(ii) Was it of the same size as the
object?
(iii) Did the image appear at  the same
distance behind the mirror as the
object was in front of it?
(iv) Could it be obtained on a screen?
Let us understand a little more about
the formation of an image by a plane
mirror in the following way:
Activity 13.3
A source of light O is placed in front
of a plane mirror PQ. Two rays OA
and OC are incident on it (Fig. 13.5).
Can you find out the direction of
the reflected rays?
Draw normals to the surface of
the mirror PQ, at the points A and
C. Then draw the reflected rays at
the points A and C. How would you
draw these rays? Call the reflected
rays AB and CD, respectively.
Extend them further. Do they meet?
Extend them backwards. Do they
meet now? If they meet, mark this
point as I. For a viewer’s eye at E
(Fig. 13 .5), do the reflected rays
(b)
Fig. 13.4 (a), (b) : Incident ray, reflected ray
and the normal at the point
of incidence lie in the same
plane
When the whole sheet of paper is
spread on the table, it represents one
plane. The incident ray, the normal at
the point of incidence and the reflected
ray are all in this plane. When you bend
the paper you create a plane different
from the plane in which the incident
ray and the normal lie. Then you do not
see the reflected ray. What does it
indicate? It indicates that the incident
ray, the normal at the point of
incidence and the reflected ray all lie
in the same plane. This is another law
of reflection.
Paheli and Boojho performed the
above activities outside the classroom
(a)
Rationalised-2023-24
SCIENCE 168
appear to come from the point I.
Since the reflected rays do not
actually meet at I, but only appear
to do so, we say that a virtual image
of the point O is formed at I. As you
have learnt already in Class VII,
such an image cannot be obtained
on a screen.
You may recall that in an image
formed by a  mirror the left of the object
appears on the right and the right
appears on the left. This is known as
lateral inversion.
13.3 Regular and Diffused
Reflection
Activity 13.4
Imagine that parallel rays are
incident on an irregular surface as
shown in Fig. 13.6. Remember that
the laws of reflection are valid at
each point of the surface. Use these
laws to construct reflected rays at
various points. Are they parallel to
one another? You will find that
these rays are reflected in different
directions. (Fig. 13.7)
When all the parallel rays reflected
from a rough or irregular surface are
not parallel, the reflection is known as
diffused or irregular reflection.
Remember that the diffused reflection
is not due to the failure of the laws of
reflection. It is caused by the
irregularities in the reflecting surface,
like that of a cardboard.
On the other hand, reflection from
a smooth surface like that of a
mirror is called regular reflection
(Fig. 13.8). Images are formed by
regular reflection.
Fig. 13.5 : Image formation in a plane mirror
Fig. 13.6 : Parallel rays incident on
an irregular surface
Fig. 13.7 : Rays reflected from irregular
surface
Fig. 13.8 : Regular reflection
Rationalised-2023-24
Page 5

LIGHT
LIGHT
T
he world is largely known through
the senses. The sense of sight
is one of the most important
senses. Through it we see mountains,
rivers, trees, plants, chairs, people and
so many other things around us. We also
see clouds, rainbows and birds flying
in the sky. At night we see the moon
and the stars. You are able to see the
words and sentences printed on this
page. How is seeing made possible?
13.1 What makes Things
Visible
Have you ever thought how we see
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
will be reflected? Let us find out.
13.2 Laws of Reflection
Activity 13.1
Fix a white sheet of paper on a
drawing board or a table. Take a
comb and close all its openings
except one in the middle. You can
use a strip of black paper for
this purpose. Hold the comb
perpendicular to the sheet of paper.
Throw light from a torch through
the opening of the comb from one
side (Fig. 13.1). With slight
adjustment of the torch and the
comb you will see a ray of light along
the paper on the other side of the
comb. Keep the comb and the torch
steady. Place a strip of plane mirror
in the path of the light ray
(Fig. 13.1). What do you observe?
After striking the mirror, the ray of
light is reflected in another direction.
The light ray, which strikes any surface,
is called the incident ray. The ray that
comes back from the surface after
reflection is known as the reflected ray.
Fig. 13.1 : Arrangement for showing reflection
Rationalised-2023-24
SCIENCE 166
A ray of light is an idealisation. In
reality, we have a narrow beam of
light which is made up of several
rays. For simplicity, we use the term
ray for a narrow beam of light.
Draw lines showing the position of
the plane mirror, the incident ray and
the reflected ray on the paper with the
help of your friends. Remove the mirror
and the comb. Draw a line making an
angle of 90º to the line representing the
mirror at the point where the incident
ray strikes the mirror. This line is known
as the normal to the reflecting surface
at that point (Fig. 13.2). The angle
Table 13.1 :Angles of Incidence
and Reflection
S. Angle of Angle of
No. Incidence (? ? ? ? ?i) Reflection (? ? ? ? ?r)
1.
2.
3.
4.
5.
Do you see any relation between the
angle of incidence and the angle of
reflection. Are they approximately equal?
If the experiment is carried out carefully,
it is seen that the angle of incidence is
always equal to the angle of reflection.
This is one of the laws of reflection.
Let us perform another activity on
reflection.
What would happen if I
threw the light on the
mirror along the normal.
Activity 13.2
Perform Activity 13.1 again. This
time use a sheet of stiff paper or a
chart paper. Let the sheet project a
little beyond the edge of the Table
(Fig. 13.4). Cut the projecting
portion of the sheet in the middle.
Look at the reflected ray. Make sure
that the reflected ray extends to the
projected portion of the paper. Bend
that part of the projected portion on
which the reflected ray falls. Can
you still see the reflected ray? Bring
the paper back to the original
Fig. 13.2 : Drawing the normal
Fig. 13.3 : Angle of incidence and angle of
reflection
Reflected
ray
Normal
Incident
ray
between the normal and incident ray is
called the angle of incidence (? ? ? ? ?i). The
angle between the normal and the
reflected ray is known as the angle of
reflection (? ? ? ? ?r) (Fig. 13.3). Measure the
angle of incidence and the angle of
reflection. Repeat the activity several
times by changing the  angle of
incidence. Enter the data  in Table 13.1.
Rationalised-2023-24
LIGHT 167
position. Can you see the reflected
ray again? What do you infer?
with the Sun as the source of light
instead of a torch. You, too, can use the
Sun as the source of light.
These activities can also be performed
by making use of the Ray Streak
Apparatus (available in the kit
prepared by NCERT).
Boojho remembered that in Class VII,
he had studied some features of the
image of an object formed by a plane
mirror. Paheli asked him to recall
those features:
(i) Was the image erect or upside
down?
(ii) Was it of the same size as the
object?
(iii) Did the image appear at  the same
distance behind the mirror as the
object was in front of it?
(iv) Could it be obtained on a screen?
Let us understand a little more about
the formation of an image by a plane
mirror in the following way:
Activity 13.3
A source of light O is placed in front
of a plane mirror PQ. Two rays OA
and OC are incident on it (Fig. 13.5).
Can you find out the direction of
the reflected rays?
Draw normals to the surface of
the mirror PQ, at the points A and
C. Then draw the reflected rays at
the points A and C. How would you
draw these rays? Call the reflected
rays AB and CD, respectively.
Extend them further. Do they meet?
Extend them backwards. Do they
meet now? If they meet, mark this
point as I. For a viewer’s eye at E
(Fig. 13 .5), do the reflected rays
(b)
Fig. 13.4 (a), (b) : Incident ray, reflected ray
and the normal at the point
of incidence lie in the same
plane
When the whole sheet of paper is
spread on the table, it represents one
plane. The incident ray, the normal at
the point of incidence and the reflected
ray are all in this plane. When you bend
the paper you create a plane different
from the plane in which the incident
ray and the normal lie. Then you do not
see the reflected ray. What does it
indicate? It indicates that the incident
ray, the normal at the point of
incidence and the reflected ray all lie
in the same plane. This is another law
of reflection.
Paheli and Boojho performed the
above activities outside the classroom
(a)
Rationalised-2023-24
SCIENCE 168
appear to come from the point I.
Since the reflected rays do not
actually meet at I, but only appear
to do so, we say that a virtual image
of the point O is formed at I. As you
have learnt already in Class VII,
such an image cannot be obtained
on a screen.
You may recall that in an image
formed by a  mirror the left of the object
appears on the right and the right
appears on the left. This is known as
lateral inversion.
13.3 Regular and Diffused
Reflection
Activity 13.4
Imagine that parallel rays are
incident on an irregular surface as
shown in Fig. 13.6. Remember that
the laws of reflection are valid at
each point of the surface. Use these
laws to construct reflected rays at
various points. Are they parallel to
one another? You will find that
these rays are reflected in different
directions. (Fig. 13.7)
When all the parallel rays reflected
from a rough or irregular surface are
not parallel, the reflection is known as
diffused or irregular reflection.
Remember that the diffused reflection
is not due to the failure of the laws of
reflection. It is caused by the
irregularities in the reflecting surface,
like that of a cardboard.
On the other hand, reflection from
a smooth surface like that of a
mirror is called regular reflection
(Fig. 13.8). Images are formed by
regular reflection.
Fig. 13.5 : Image formation in a plane mirror
Fig. 13.6 : Parallel rays incident on
an irregular surface
Fig. 13.7 : Rays reflected from irregular
surface
Fig. 13.8 : Regular reflection
Rationalised-2023-24
LIGHT 169
Let us find out.
13.4 Reflected Light Can be
Reflected Again
Recall the last time you visited a hair
dresser. She/he makes you sit in front of
a mirror. After your hair cut is complete,
she/he holds a mirror behind you to show
you how the hair has been cut
(Fig. 13.9). Do you know how you could
Paheli recalls having constructed a
periscope as an Extended Activity in
Class VI. The periscope makes use of
two plane mirrors. Can you explain
how reflection from the two mirrors
enables you to see objects which are
not visible directly? Periscopes are
used in submarines, tanks and also
by soldiers in bunkers to see things
outside.
13.5 Multiple Images
You are aware that a plane mirror forms
only a single image of an object. What
happens if two plane mirrors are used
in combination? Let us see.
Do We See all Objects due to Reflected Light?
Nearly everything you see around is seen due to reflected light. Moon, for example,
receives light from the Sun and reflects it. That’s how we see the moon. The objects
which shine in the light of other objects are called illuminated objects. Can you
name some other such objects?
There are other objects, which give their own light, such as the Sun, fire, flame
of a candle and an electric lamp. Their light falls on our eyes. That is how we see
them. The objects which emit their own light are known as luminous objects.
Fig. 13.9 : Mirror at the hair dresser shop
I have a question. Can the
reflected rays be further reflected
if incident on another mirror?
Rationalised-2023-24
```

## Science & Technology for UPSC CSE

165 videos|338 docs|324 tests

## FAQs on NCERT Textbook: Light - Science & Technology for UPSC CSE

 1. What is light and how is it produced?
Ans. Light is a form of energy that enables us to see things around us. It is produced when an object vibrates and its atoms emit energy in the form of electromagnetic waves. This energy travels through space at a constant speed of 3 x 10^8 meters per second and can be seen by our eyes as different colors.
 2. How does light travel and what are its properties?
Ans. Light travels in a straight line and can be reflected, refracted, and absorbed. It also has properties such as wavelength, frequency, and speed. Wavelength is the distance between two consecutive peaks of a wave, frequency is the number of waves that pass a point in one second, and speed is the rate at which light travels through space.
 3. What is the difference between reflection and refraction of light?
Ans. Reflection is the bouncing back of light from a surface, while refraction is the bending of light as it passes through a different medium. The angle of incidence (angle between the incident ray and the normal) is equal to the angle of reflection (angle between the reflected ray and the normal) in reflection, while in refraction, the angle of incidence is not equal to the angle of refraction (angle between the refracted ray and the normal).
 4. How does light interact with objects and what are the different types of objects?
Ans. Light can interact with objects in three ways - it can be absorbed, transmitted, or reflected. Objects can be classified into opaque, translucent, and transparent based on how much they allow light to pass through them. Opaque objects do not allow any light to pass through them, translucent objects allow some light to pass through them, and transparent objects allow all light to pass through them.
 5. What are the different colors of light and how are they produced?
Ans. The different colors of light are produced by different wavelengths of light. The colors of the visible spectrum are red, orange, yellow, green, blue, indigo, and violet. When white light passes through a prism, it gets split up into these colors due to their different wavelengths. The color of an object is the color of light that it reflects, and the color that it absorbs is the color that it appears to be.

## Science & Technology for UPSC CSE

165 videos|338 docs|324 tests

### Up next

 Explore Courses for UPSC exam

### How to Prepare for UPSC

Read our guide to prepare for UPSC which is created by Toppers & the best Teachers
Signup to see your scores go up within 7 days! Learn & Practice with 1000+ FREE Notes, Videos & Tests.
10M+ students study on EduRev
Track your progress, build streaks, highlight & save important lessons and more!
Related Searches

,

,

,

,

,

,

,

,

,

,

,

,

,

,

,

,

,

,

,

,

,

;