In this ppt you will study about light. for Ex what is light and many more thing specially for class seventh and eights CBSE .

1. 1Light

2. 4WHAT IS LIGHT ?
2Light

3. LATERAL INVERSION
3Light
For Example You are the object and
what you see in mirror is your
image. You are identical to your
image as seen in the mirror. In case
of a plane mirror the image formed
is erect and same size as the object.
But there is one difference is in your
left and right. When you move your
right hand, in the image it seems as
if your left hand is moving. This is
called lateral inversion, where left
appear be right and right appears to
be left.

4. Light 4
REFLECTING THROUGH SPHERICAL
MIRRORS
If the reflecting surface of
a spherical mirror is
concave, it is called as a
concave mirror. If the
reflecting surface of a
spherical mirror is convex,
it is called a convex
mirror.

5. USES OF SPHERICAL MIRRORS
Convex mirror
Concave mirror
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Convex mirror
Convex are mainly use at rear side of a car on
driver’s side of a car isa convex mirror. In some
countries, these are labelled with safety warning ,
to warm the driver of the convex mirror’s distorting
effects on actualdistance of the vehicle behindthe
driver

6. Light 6
Concave
mirror

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LAWS OF REFLECTION
•Incident ray – The light ray falling on any
surface is called the incident ray.
•Reflected ray- The light ray that comes
back after reflection is called the reflected
ray.
•Normal ray – The line perpendicular to
the reflecting surface is called the normal
ray.
•Angle of incidence – The angle between
the incident ray and the normal ray is
called the angle of incidence.
•Angle of reflection – the angle between
the reflected ray and the normal ray is
called the angle of reflection.

8. Light 8
REGULAR AND IRREGULAR REFLECTION
The Laws of reflection are valid for
reflection from all shiny surfaces.
Thus the angle of incidence has to
be equal to the angle of reflection
in each case. It is just that the rays
reflected from an irregular surface
are unparallel rays. When the rays
reflected from a plane surfaces are
not parallel, the reflection is known
irregular reflection.
irregular reflection

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regular reflection
On the other hand,
reflection of light rays
from a smooth surface
like that of a plane mirror
is called a regular
reflection Images formed
by regular reflection.

10. Light 10
MULTIPLE REFLECTIONS
To predict the path of
incident rays for this case,
we need to apply the laws
of reflection again.
However, at the same time,
understand that when two
mirrors are placed at an
angle the rays of light are
reflected multiple times
through them. For instance,
when two mirrors are set
parallel facing each other
they will create the illusion
that the image of the
object repeats forever.

11. Light 11
KALEIDOSCOPE –
AN ILLUSTRATION OF
MULTIPLE REFLECTION
The kaleidoscopealsouses
multiplereflections through
mirrors to form beautiful
patterns.

12. SUNLIGHT AND ITS COLOURS
• The seven coloursare violet,
indigo,blue, green, yellow,
orange andred. All thisspectrum
of colours we can perform this
simpleactivity.
Light 12

13. THE HUMAN EYE
The human eye a sense organ. It helps in seeing different
objects. The light reflected from different objects enter
our eyes and thus we can see things around us. It is an
important organ. So, understandings its structure is also
very important.
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14. The human eye has a nearly spherical shape, and is
about an inch in diameter. The white portion visible from
outside is the cornea. Behind the cornea is a space filled
with a liquid known as aqueous humour. Further behind
is a crystalline lens. Between the aqueous humour and
the lens is the iris, a muscular diaphragm which has a
small hole in it known as the pupil. The pupil usually
appears black, and controls the amount of light entering
the eye.
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15. ACCOMODATION OF THE EYE
The eye focuses on different objects by changing the
radius of curvature of the lens. The cilliary muscles
relax to view distant objects and contract to focus
on nearby objects. This is knows as the power of
accommodation of the eye. However, the muscles
cannot be strained beyond a limit and hence if the
objects is placed too close to your eyes the image
formed on the retina would be blurred
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16. PERSISTENCE OF VISION
The imageof an object formed in retina does
not vanish immediately;it stays for 1/16
second. This is called as thepersistence of
vision. Any imagethatis flashedmore than
16 images per second would be seenas
moving.
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17. DEFFECTS OF THE HUMAN EYE
At times, the eye lens cannot focus even when the
objects is placed beyond 25cm. Some people
cannot see nearby objects clearly and see nearby
objects clearly and see distant objects clearly. This
defect ;is called hypermetropia. There are also
people who can see nearby objects clearly but
face a problem viewing far-off objects. This defect
is called myopia. Thus for such cases the eye lens
has to be corrected using other lenses, and the
doctor asks you to wear spectacles.
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18. Light 18

19. CARE OF YOUR EYES
• You should have regular checkup for
your eyes. If there is any problem,
you should go to an eye specialist. If
advised, use suitable spectacles.
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20. • Never look directly into a
very bright source of light,
like the sun. It can
damage the retina of the
eye.
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21. • Never rub your eyes if
some particles dust go
into your eyes, wash
your eyes with clean
water. In case there is no
improvement, visit a
doctor.
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22. • Wash your eyes frequently with clean
water.
• Always read at the normal distance for
vision. Do not read by bringing your book
too close to your eyes or keeping it too
far. Always read under proper light.
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23. • Do not read in a moving vehicle.
• Avoid watching television or working on
the computer for long sessions always
take a break to rest your eyes.
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24. SCRIPT FOR THE VISUALLY
CHALLENGED: THE BRAILLE SYSTEM
• The Braille system is a method thatis widely used by visually
challengedpeople to read and write. It was devised in 1821
by Louis Braille, a blind Frenchmen.Visually challenged
people feel thedots to identify thecharacter writtenin Braille
system.
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25. Light 25

26. Light 26