LIGHT 6
CHAPTER
& changes when it travels from one medium to
another.
CONTENTS
The wavelength () of light changes when it goes
Sources of light from one medium to another.
Medium of light The frequency (f) of the light wave remains the
same in all media.
Reflection of light
Light gets reflected back from polished surfaces,
Laws of reflection & nature of image such as mirrors, polished metal surfaces, etc.
Regular & diffused reflection Light undergoes refraction (bending) when it
Characteristics of the image travels from one transparent medium to another.
formed by plane mirror
Multiple reflection SOURCES OF LIGHT
Reflection from spherical mirror
The objects which emit (give) light are called
Rule of Image formation by
luminous objects. It may be natural or man-
spherical mirror
made. Sun is a natural source of light and electric
Refraction of light
lamp, and oil lamp, etc. are man-made source of
Spherical lens light.
Rules of Image formation by The Non-luminous objects do not emit light.
spherical lens However, such objects become visible due to the
Total internal reflection reflection of the light falling on them. Moon does
Dispersion of white light by a not emit light & becomes visible due to the
reflection of the sunlight falling on it.
glass prism
Human eye
MEDIUM OF LIGHT
Defects of vision, symptoms and
Substance through which light propagates or tends
remedy (correction)
Refraction in nature to propagate is called a medium of light.
According to the medium of light objects are
Scattering of light
divided into three parts.
(i) Transparent object :
Bodies that allow light to pass through then i.e.
transmit light through them, are called transparent
bodies.
INTRODUCTION Ex. Glass, water, air etc
(ii) Translucent object :
Light is a form of energy, (optical energy) which
Bodies that can transmit only a part of light
helps us in seeing objects by its presence.
through them are called translucent objects.
Light is an electromagnetic wave & travels in a
Ex. Froasted or ground glass, greased paper , paraffin
straight line with the speed 3 × 108 m/s in vacuum
wax etc.
,(iii) Opaque object : Angle of reflection : The angle that the reflected
Bodies that do not allow light to pass through ray makes with the normal, is called the angle of
them at all are said to be opaque objects reflection. It is represented by the symbol r. In
Ex. Chair, desk etc. diagram, QON is the angle of reflection.
REFLECTION OF LIGHT LAWS OF REFLECTION & NATURE
OF IMAGE
When light rays are incident on an opaque
polished surface (medium), these are returned First law : The incident ray, the reflected ray and
back in the same medium. This phenomenon of the normal at the point of incidence, all lie in the
returning of ray of light in the same medium, is same plane.
called reflection of light. Second law : The angle of reflection (r) is
always equal to the angle of incidence (i).
SOME ASSOCIATED TERMS i.e., r = i
(For normal incidence, i = 0, r = 0. The ray is
P N Q reflected back along normal).
NATURE OF IMAGE
i r Incident rays starting from a point object, and
reflected from a mirror, either actually meet at or
X Y appear to come from a point. The other point is
O called the image of the point object.
Reflecting surface : The surface from which the Real Image Virtual Image
light is reflected, is called the reflecting surface. 1. A real image is formed 1. A virtual image is
In diagram, XY is the reflecting surface. when two or more formed when two or
(Actually XY is the section of a reflecting reflected rays meet at more rays appear to
surface, made by the plane of the book page a point in front of the be coming from a point
mirror. behind the mirror.
which is perpendicular to it.)
Point of incidence : The point on the reflecting 2. A real image can be 2. A virtual image cannot
obtained on a screen. be obtained on a screen.
surface at which a ray of light strikes, is called the
point of incidence. In diagram, O is the point of 3. A real image is inverted 3. A virtual image is erect
incidence. with respect to the with respect to the
Normal : A perpendicular drawn on the reflecting object. object.
surface at the point of incidence, is called the
normal. In diagram, NO is the normal. REGULAR & DIFFUSED REFLECTION
Incident ray : The ray of light which strikes the
Regular Reflection :
reflecting surface at the point of incidence is
In this reflection, parallel beam of light goes
called the incident ray. In diagram, PO is the parallel after reflection from plane surface.
incident ray. This reflection follows the laws reflection.
Reflected ray : The ray of light reflected from the
reflecting surface from the point of incidence, is
called the reflected ray. In diagram, OQ is the
reflected ray.
Angle of incidence : The angle that the incident
ray makes with the normal, is called the angle of
incidence. It is represented by the symbol i. In
diagram, angle PON is the angle of incidence.
Regular reflection
, IRREGULAR REFLECTION OR DIFFUSED If there are two plane mirrors inclined to each
REFLECTION : other at an angle 90° , the number of images of a
In this reflection, parallel beam of light goes point object formed are 3.
random after reflection from a rough surface.
KALEIDOSCOPE
This reflection also follows the laws of reflection.
This is a structure made up of three plane mirrors
in which all the plane mirrors are joint along the
length and arranged at an angle of 60º as shown in
figure.
A cardboard tube is wrapped around the mirrors
to form a tublar structure. One end of this tube is
pasted with transparent sheets with some multi
coloured beads or pieces of broken bangles in
Irregular or diffused reflection between these sheets. Another and is closed with
a plane transparent sheet.
Note : Laws of reflection are always valid no When we observe through the transparent end
matter whether reflection is regular or irregular. with rotating the tube beautiful coloured pattern.
The above pattern is because of multiple
CHARACTERISTICS OF THE IMAGE reflection of light rays coming from small beads
FORMED BY PLANE MIRROR and pieces of bangles.
Size : size of the image is same as that of object. 60°
Upright or Erect : Image formed erect with 60° 60°
Tube
respect to object. Mirror
Image distance : It will be same as that of object Mirror
Coloured
distance. beads
Lateral inversion : If you move your right hand,
it will appear as if the left hand of your image is
moving. If you keep a printed page in front of a REFLECTION FROM SPHERICAL MIRROR
plane mirror, the image of the letters appear erect
but inverted laterally, or sideways. Such an There are two types of spherical mirrors:
inversion is called lateral inversion. (i) Concave mirror :
A
L R R L
Principal
axis
C
F P
Object Image
B
MULTIPLE REFLECTION (ii) Convex mirror :
A
Number of images formed by combination of plane
mirrors depends upon angle between mirrors. Principal
axis
P F C
90°
B
CHAPTER
& changes when it travels from one medium to
another.
CONTENTS
The wavelength () of light changes when it goes
Sources of light from one medium to another.
Medium of light The frequency (f) of the light wave remains the
same in all media.
Reflection of light
Light gets reflected back from polished surfaces,
Laws of reflection & nature of image such as mirrors, polished metal surfaces, etc.
Regular & diffused reflection Light undergoes refraction (bending) when it
Characteristics of the image travels from one transparent medium to another.
formed by plane mirror
Multiple reflection SOURCES OF LIGHT
Reflection from spherical mirror
The objects which emit (give) light are called
Rule of Image formation by
luminous objects. It may be natural or man-
spherical mirror
made. Sun is a natural source of light and electric
Refraction of light
lamp, and oil lamp, etc. are man-made source of
Spherical lens light.
Rules of Image formation by The Non-luminous objects do not emit light.
spherical lens However, such objects become visible due to the
Total internal reflection reflection of the light falling on them. Moon does
Dispersion of white light by a not emit light & becomes visible due to the
reflection of the sunlight falling on it.
glass prism
Human eye
MEDIUM OF LIGHT
Defects of vision, symptoms and
Substance through which light propagates or tends
remedy (correction)
Refraction in nature to propagate is called a medium of light.
According to the medium of light objects are
Scattering of light
divided into three parts.
(i) Transparent object :
Bodies that allow light to pass through then i.e.
transmit light through them, are called transparent
bodies.
INTRODUCTION Ex. Glass, water, air etc
(ii) Translucent object :
Light is a form of energy, (optical energy) which
Bodies that can transmit only a part of light
helps us in seeing objects by its presence.
through them are called translucent objects.
Light is an electromagnetic wave & travels in a
Ex. Froasted or ground glass, greased paper , paraffin
straight line with the speed 3 × 108 m/s in vacuum
wax etc.
,(iii) Opaque object : Angle of reflection : The angle that the reflected
Bodies that do not allow light to pass through ray makes with the normal, is called the angle of
them at all are said to be opaque objects reflection. It is represented by the symbol r. In
Ex. Chair, desk etc. diagram, QON is the angle of reflection.
REFLECTION OF LIGHT LAWS OF REFLECTION & NATURE
OF IMAGE
When light rays are incident on an opaque
polished surface (medium), these are returned First law : The incident ray, the reflected ray and
back in the same medium. This phenomenon of the normal at the point of incidence, all lie in the
returning of ray of light in the same medium, is same plane.
called reflection of light. Second law : The angle of reflection (r) is
always equal to the angle of incidence (i).
SOME ASSOCIATED TERMS i.e., r = i
(For normal incidence, i = 0, r = 0. The ray is
P N Q reflected back along normal).
NATURE OF IMAGE
i r Incident rays starting from a point object, and
reflected from a mirror, either actually meet at or
X Y appear to come from a point. The other point is
O called the image of the point object.
Reflecting surface : The surface from which the Real Image Virtual Image
light is reflected, is called the reflecting surface. 1. A real image is formed 1. A virtual image is
In diagram, XY is the reflecting surface. when two or more formed when two or
(Actually XY is the section of a reflecting reflected rays meet at more rays appear to
surface, made by the plane of the book page a point in front of the be coming from a point
mirror. behind the mirror.
which is perpendicular to it.)
Point of incidence : The point on the reflecting 2. A real image can be 2. A virtual image cannot
obtained on a screen. be obtained on a screen.
surface at which a ray of light strikes, is called the
point of incidence. In diagram, O is the point of 3. A real image is inverted 3. A virtual image is erect
incidence. with respect to the with respect to the
Normal : A perpendicular drawn on the reflecting object. object.
surface at the point of incidence, is called the
normal. In diagram, NO is the normal. REGULAR & DIFFUSED REFLECTION
Incident ray : The ray of light which strikes the
Regular Reflection :
reflecting surface at the point of incidence is
In this reflection, parallel beam of light goes
called the incident ray. In diagram, PO is the parallel after reflection from plane surface.
incident ray. This reflection follows the laws reflection.
Reflected ray : The ray of light reflected from the
reflecting surface from the point of incidence, is
called the reflected ray. In diagram, OQ is the
reflected ray.
Angle of incidence : The angle that the incident
ray makes with the normal, is called the angle of
incidence. It is represented by the symbol i. In
diagram, angle PON is the angle of incidence.
Regular reflection
, IRREGULAR REFLECTION OR DIFFUSED If there are two plane mirrors inclined to each
REFLECTION : other at an angle 90° , the number of images of a
In this reflection, parallel beam of light goes point object formed are 3.
random after reflection from a rough surface.
KALEIDOSCOPE
This reflection also follows the laws of reflection.
This is a structure made up of three plane mirrors
in which all the plane mirrors are joint along the
length and arranged at an angle of 60º as shown in
figure.
A cardboard tube is wrapped around the mirrors
to form a tublar structure. One end of this tube is
pasted with transparent sheets with some multi
coloured beads or pieces of broken bangles in
Irregular or diffused reflection between these sheets. Another and is closed with
a plane transparent sheet.
Note : Laws of reflection are always valid no When we observe through the transparent end
matter whether reflection is regular or irregular. with rotating the tube beautiful coloured pattern.
The above pattern is because of multiple
CHARACTERISTICS OF THE IMAGE reflection of light rays coming from small beads
FORMED BY PLANE MIRROR and pieces of bangles.
Size : size of the image is same as that of object. 60°
Upright or Erect : Image formed erect with 60° 60°
Tube
respect to object. Mirror
Image distance : It will be same as that of object Mirror
Coloured
distance. beads
Lateral inversion : If you move your right hand,
it will appear as if the left hand of your image is
moving. If you keep a printed page in front of a REFLECTION FROM SPHERICAL MIRROR
plane mirror, the image of the letters appear erect
but inverted laterally, or sideways. Such an There are two types of spherical mirrors:
inversion is called lateral inversion. (i) Concave mirror :
A
L R R L
Principal
axis
C
F P
Object Image
B
MULTIPLE REFLECTION (ii) Convex mirror :
A
Number of images formed by combination of plane
mirrors depends upon angle between mirrors. Principal
axis
P F C
90°
B
