15 Light
You will learn about
Light is an integral part of our lives, and yet we take
it for granted quite a bit. All the time, during day or .Whatmakes things visible
.Reflection
night, we depend on natural orartifncial lighting. Dispersion
Look at the pictures below and answer the Human eye
questions that follow.
1 2. 3 4.
1. Of the objects shown in picture 1, pick out the objects that make it possible for us to
see' things around us.
2. In picture 2, the girl can see her image in the plate on the left, but not in the plate on
the right. Why do you think this is so?
3. In which hand is the boy wearing the wrist watch in the two pictures?
4. Why are the two people wearing spectacles? What do you think will happenif they
exchange their spectacles?
Light does not just exist. It is produced by a source, from where it travels outwards and
bounces off or gets absorbed by objects in its path. We see light only when it reaches our
eyes. In most cases, some of the light falling on an object is always reflected by it. That is
how we can see it. Sometimes, we can see our image in the reflected light and at other
times, we cannot. We can see things around us only when there is a source of light. When
all sources of light are switched of, it gets pitch dark and we can see nothing.
The images produced by reflection have many interesting characteristics, we will study
some of them in this chapter. we Will also learn how we see with our eyes, how some eye
defects can be corrected, and how we can take care of our eves.
sajpejads Jjayi a8ueyxa Aau
H Aueajp aas o1 a1qe aq 10u |IM Aui 793]s-aA3Jjy) u! 198jap e jpaJu03 0] sajpeads Buueem aJe AauL 'puey 4
SIy uo si yoem 1sum ayi yBnosi se syo0 ! 'eaeuj ay uj inq 'puey yaj sy uo yojem 1sum as) uueam SI Aoq L E
'po sI a1ejd aya 'ana>id puopas au) uj pue Mau s 81Pjd au 'aunjd 1suy aya u z 'saka uno 'ung ay 'dwej auu T
, MAKES THINGS VISIBLE?
WHAT T
v ek n o w ,
that all objects that we see can be
Iminous, classified into two types: luminous and non-
s objects are thOse that emit light on
m the sun, the stars, and a light their own. These are also called
sOur
bulb). Non-luminous
ghtht on their own (e.g, a table, a chair, not
objects
and a tree) and are seen
are those to
nt
sOurce of liaht. These objects cannot be in the presence
seen in pre>* ofa
seen if there is no light source.
luminous ODjects dre seen
when light from luminous obiects falls
afrom a light source bounces off on them. Lignt
con
a non-luminous object and enters o u r eyes. When
af light enter our eyes, they fall on a
light-sensitive d
etina. They are then transmitted to the brain throughlaver at the back eye caiE of the
the.
the optic around us. f the
nerves, and the
Da
orOrets the image rormed on the retina. This is how we 'see' objects
hiect is a source oT Iight, then we can see it from the light it emits. If the object is nota
cource of Ilight, then we see it from the light it reflects (from a source of light). We also see
he moon and the planets because they reflect light rays of the sun.
REFLECTION
AN
When a ray of light hits a mirror, or any surface, it bounces off the surface. This phenomenon
is called reflection of light. While light is reflected from any surface, reflection from a mirroor
or any other highly polished surface (such as metal or polished granite) produces an image
that we can see. When you look at a mirror, you see the reflection of other things around you
along with your own image. Let us perform an activity to learn more about this phenomenon.
Activity
Aim: To study the nature of reflection from a mirror
Materials needed: A4 size paper, a pair of scissors, adhesive tape, and a wall mirror
(bathroom mirror, dressing mirror, etc.)
Method:
1. Fold the A4 size paper in the middle, lengthwise.
2. Cut out a thin slit on the fold, leaving out 1 inch on the top and bottom of the paper.
3. Open out the paper and stick it on a mirror
4 Look at yourself in the mirror through the slit in the paper. Make a note of the various
objects that you can see behind you.
5. Now move to your right and look at the mirror through the slit. Try out various positions.
Try to see along the surface of the mirror. Make a note of the images that you see at the
various positions of your eye.
Observation: You will notice that you will be able to see yourself only if you are directiy in front
of the slit. If you move to the right, you will be able to see the image of things to your left. If you
move further to the right, you will be able to see things further to your left.
Light
225
, us in a scientific
manner by drawinn
rawing a
Let put down our observations from the activitythat makes an angle of 90) to the
he
diagram. First draw a line perpendicular (i.e., a line
e an
point where the slit is located (Fia. 15.1). This line, SN, is called the normal. mirrora
Reflecting surface of the miror
lllll7lIllls/7lll
Fig. 15.1 Refilection from a plane mirror
The rays of light that come from the object and hit the mirror are called incident
rays. In
Figure 15.1, AS and BS are incident rays. The rays of light that get reflected from (.e.,
off) the mirror are called reflected rays. In bounce
Figure 15.1, SA' and SB' are reflected rays
The point at which the incident
ray hits the mirror is called the point of incidence. In
15.1, Sis the point of incidence. A normal drawn to the mirror Figure
at the point of incidence is
called a normal at the point of incidence. The
is called the angle of
angle between the incident ray and the normal
incidence. Figure 15.1, angle ASN is the angle of incidence of the
In
incident ray AS. The angle between the reflected ray and the
normal is called the angle
reflection. In Figure 15.1, the angle of reflection of the of
reflected ray isSA' NSA:
Laws of Reflection
InFigure 15.1, the image of an object at A could be seen at A'and
the image of an
Bcould be seen at B. What conclusions can
you draw from this
object at
observation? Look
the angle of incidence and the
corresponding angles of reflection. You will see thatclosely at
case, the angle of incidence equals the in each
angle of reflection. Also, the incident
ray,and the normal at the point of incidence lie on the ray, the reflected
known as the laws of reflection and are same plane. These two statements are
summarized below
First law The incident ray, the reflected
ray, and the normal at the
the same plane. point of incidence
lie on
Second law The angle of incidence is equal to the
angle of reflection.
226 Light
You will learn about
Light is an integral part of our lives, and yet we take
it for granted quite a bit. All the time, during day or .Whatmakes things visible
.Reflection
night, we depend on natural orartifncial lighting. Dispersion
Look at the pictures below and answer the Human eye
questions that follow.
1 2. 3 4.
1. Of the objects shown in picture 1, pick out the objects that make it possible for us to
see' things around us.
2. In picture 2, the girl can see her image in the plate on the left, but not in the plate on
the right. Why do you think this is so?
3. In which hand is the boy wearing the wrist watch in the two pictures?
4. Why are the two people wearing spectacles? What do you think will happenif they
exchange their spectacles?
Light does not just exist. It is produced by a source, from where it travels outwards and
bounces off or gets absorbed by objects in its path. We see light only when it reaches our
eyes. In most cases, some of the light falling on an object is always reflected by it. That is
how we can see it. Sometimes, we can see our image in the reflected light and at other
times, we cannot. We can see things around us only when there is a source of light. When
all sources of light are switched of, it gets pitch dark and we can see nothing.
The images produced by reflection have many interesting characteristics, we will study
some of them in this chapter. we Will also learn how we see with our eyes, how some eye
defects can be corrected, and how we can take care of our eves.
sajpejads Jjayi a8ueyxa Aau
H Aueajp aas o1 a1qe aq 10u |IM Aui 793]s-aA3Jjy) u! 198jap e jpaJu03 0] sajpeads Buueem aJe AauL 'puey 4
SIy uo si yoem 1sum ayi yBnosi se syo0 ! 'eaeuj ay uj inq 'puey yaj sy uo yojem 1sum as) uueam SI Aoq L E
'po sI a1ejd aya 'ana>id puopas au) uj pue Mau s 81Pjd au 'aunjd 1suy aya u z 'saka uno 'ung ay 'dwej auu T
, MAKES THINGS VISIBLE?
WHAT T
v ek n o w ,
that all objects that we see can be
Iminous, classified into two types: luminous and non-
s objects are thOse that emit light on
m the sun, the stars, and a light their own. These are also called
sOur
bulb). Non-luminous
ghtht on their own (e.g, a table, a chair, not
objects
and a tree) and are seen
are those to
nt
sOurce of liaht. These objects cannot be in the presence
seen in pre>* ofa
seen if there is no light source.
luminous ODjects dre seen
when light from luminous obiects falls
afrom a light source bounces off on them. Lignt
con
a non-luminous object and enters o u r eyes. When
af light enter our eyes, they fall on a
light-sensitive d
etina. They are then transmitted to the brain throughlaver at the back eye caiE of the
the.
the optic around us. f the
nerves, and the
Da
orOrets the image rormed on the retina. This is how we 'see' objects
hiect is a source oT Iight, then we can see it from the light it emits. If the object is nota
cource of Ilight, then we see it from the light it reflects (from a source of light). We also see
he moon and the planets because they reflect light rays of the sun.
REFLECTION
AN
When a ray of light hits a mirror, or any surface, it bounces off the surface. This phenomenon
is called reflection of light. While light is reflected from any surface, reflection from a mirroor
or any other highly polished surface (such as metal or polished granite) produces an image
that we can see. When you look at a mirror, you see the reflection of other things around you
along with your own image. Let us perform an activity to learn more about this phenomenon.
Activity
Aim: To study the nature of reflection from a mirror
Materials needed: A4 size paper, a pair of scissors, adhesive tape, and a wall mirror
(bathroom mirror, dressing mirror, etc.)
Method:
1. Fold the A4 size paper in the middle, lengthwise.
2. Cut out a thin slit on the fold, leaving out 1 inch on the top and bottom of the paper.
3. Open out the paper and stick it on a mirror
4 Look at yourself in the mirror through the slit in the paper. Make a note of the various
objects that you can see behind you.
5. Now move to your right and look at the mirror through the slit. Try out various positions.
Try to see along the surface of the mirror. Make a note of the images that you see at the
various positions of your eye.
Observation: You will notice that you will be able to see yourself only if you are directiy in front
of the slit. If you move to the right, you will be able to see the image of things to your left. If you
move further to the right, you will be able to see things further to your left.
Light
225
, us in a scientific
manner by drawinn
rawing a
Let put down our observations from the activitythat makes an angle of 90) to the
he
diagram. First draw a line perpendicular (i.e., a line
e an
point where the slit is located (Fia. 15.1). This line, SN, is called the normal. mirrora
Reflecting surface of the miror
lllll7lIllls/7lll
Fig. 15.1 Refilection from a plane mirror
The rays of light that come from the object and hit the mirror are called incident
rays. In
Figure 15.1, AS and BS are incident rays. The rays of light that get reflected from (.e.,
off) the mirror are called reflected rays. In bounce
Figure 15.1, SA' and SB' are reflected rays
The point at which the incident
ray hits the mirror is called the point of incidence. In
15.1, Sis the point of incidence. A normal drawn to the mirror Figure
at the point of incidence is
called a normal at the point of incidence. The
is called the angle of
angle between the incident ray and the normal
incidence. Figure 15.1, angle ASN is the angle of incidence of the
In
incident ray AS. The angle between the reflected ray and the
normal is called the angle
reflection. In Figure 15.1, the angle of reflection of the of
reflected ray isSA' NSA:
Laws of Reflection
InFigure 15.1, the image of an object at A could be seen at A'and
the image of an
Bcould be seen at B. What conclusions can
you draw from this
object at
observation? Look
the angle of incidence and the
corresponding angles of reflection. You will see thatclosely at
case, the angle of incidence equals the in each
angle of reflection. Also, the incident
ray,and the normal at the point of incidence lie on the ray, the reflected
known as the laws of reflection and are same plane. These two statements are
summarized below
First law The incident ray, the reflected
ray, and the normal at the
the same plane. point of incidence
lie on
Second law The angle of incidence is equal to the
angle of reflection.
226 Light
