2. INTRODUCTION TO LIGHT
• 𝕃𝕀𝔾ℍ𝕋
• Light is a form of energy. Light is needed to see things around us.
• WHAT MAKES LIGHT VISIBLE
• -We see various things (Or objects) around us with our eyes but eyes
alone cannot see anyobject.
• -we need a source of light to make the object (Or things) visible.
• -It is only when light coming from an object enters our eyes that we see
that object.
3. Light:~
• -This light may have emitted by the object itself or may have been reflected by the
object.
• - It is light which makes things visible to us. Light enables us to see things from which it
comes or from which it is reflected.
• Let’s see an example.....
• Here sunlight fall on object (flower)
The flower reflect sunlight in all
Direction sunlight reflect by flower
Enters our eyes this is how we see..
4. Luminous and Non luminousobject
• LUMINOUS OBJECT
• -The objects which emit their own light are called luminous object .
• - luminous objects produce their own light and then emit this light.
• - for example: the sun, other star etc.
• NON- LUMINOUS OBJECT
• - The object which do not emit their own light is called non- luminous object.
• - The non-luminous object cannot make their own light.
• - for example: the moon , earth,other planets, etc.
5. Reflection of lightand lawsof light
• REFLECTION OF LIGHT
• - The process of sending back light rays which fall on the surface of an object, is called reflection of
light.
• - Ray-box acts as a source of light in the ‘ reflection of might activities.
• THE LAWS OF REFLECTION
• 1. The ray of light which falls on the mirror surface is called Incident ray .
• 2. The point at which the incident ray stricks the mirror is called the point of incidence.
• 3.the ray of light which is sent back by the mirror is called the reflected ray.
• 4.the ‘normal’ is a line drawn at right angles to the mirror surface at the point of incidence.
• 5. The angle between incident ray and normal is called the angel of incidence.
• 6. The angel between reflected ray and normal is called the angel of reflection.
6. Regularreflection
• REGULAR REFLECTION
• - In regular reflection, a parallel beam of incident light is reflected as a
parallel beam in one direction.
• - Regular reflection of light occurs from smooth surface like that of a
plane mirror ( or highly polished metal surface).
• - A plane mirror produces regular reflection of light.
7. Diffusereflection
• DIFFUSE REFLECTION OF LIGHT
• - In diffuse reflection, a parallel beam of incident light is reflected in different directions.
• - The diffuse reflection of light takes place from rough surfaces like that of paper,
cardboard, chalk, table, chair, walls, and unpolished metal objects.
• - A sheet of papers produce diffuse reflection of light.
• -The diffuse reflection of light is not due to the failure of the laws of reflection.
• - Most of the objects around us cause diffuse reflection of light and scatter the light
falling on them in all directions.
8. Multiple images
• *Multiple images*
• • when two plane mirrors are kept in cleaned at an angle, they can form
multiple images of an object.This is because the image of object formed
in one plane mirror acts as object for the other plane mirror.
• •If an object is placed between two parallel planes mirror facing each
other,than theoretically infinite number of (images) should.
9. Kaleidoscope
*kaleidoscope
• The Kaleidoscope is an instrument or toy containing inclined plane
mirror which produce multiple reflection of coloured glass pieces (or
coloured plastic pieces) and create beautifully pattern.
•An interesting feature of a kaleidoscope is that we can never see the same
pattern again. Every time a new pattern is formed. Kaleidoscope are used
by designer of wall paper and fabrics as well as by artist to get ideas for
new patterns.
11. Sunlightwhiteorcoloured
• *Sunlight –white or coloured*
• •The sunlight referred to as white light .
• •The white sunlight actually consists of seven colours (mixed together).
•
• ACTIVITY
• The Splitting you up of white light into seven prism is called dispersion
Of light
12. Dispersion of light
• The formation of spectrum (band of seven colours ) shows that white
sunlight is made up of seven colours. The seven colours of the spectrum
of white light are: violet,indigo,blue green, yellow , orange and red.
• Rainbow in the sky natural phenomena showing the dispersion of
sunlight .Rinavow is produced by the dispersion of sunlight by tiny rain
drops suspended in the atmosphere (which act as tiny prismade if
water.)The formation of rainbow also tells us that sunlight consists of
seven colours .
14. • EYE ; THE HUMAN EYE
• The human eye
•
• Eye one of the important sense organ.
• The eye enable us to see various object around us.
• The main parts of human eye are: cornea, Iris, pupil, ciliary muscles, Eye
lens( which is a flexible convex lens), Retina and Optic nerve.
15. Function of theeye
• Working of the eye
• When we look at an object, the light rays coming from the object enter the pupil and fall on the eye
lens.
• The eye lens is a convex lens so it coverage the light rays and produce a real and inverted image of
the object on the retina.
• The Retina has a large number of light sensitive cells.
• When the image of the object falls on the retina then the light sensitive cell generated electrical signal.
• he Retina sends these electrical signal to the brain throw the optic nerve and we are able to see the
object.
• -NOTE:-The image of an object formed on the retina is inverted but our brain interprets this image as
that of an erected object.
16. Function of Iris and pupil
• *The function of Iris and pupil*
•
• •The iris automatically adjust the size of pupil according to the intensity of light received by the
eye from the surroundings.
• •If the amount of light around us is very high (as during the day light) then it is contract the
pupil (make the pupil small )and hence reduce the amount of light entering the eye.
• •On the other hand if the amount of light around us its small (as in a dark room or during the
night) then Iris expand the pupil (make the pupil large) so that more light can enter the eye.
• •The adjustment of size of pupil takes some time.
19. Rods and cones
•The retina of our eye has a large number of light sensitive cells.There are two kind of
sensitive cell in retina rods and cones.
(1) Rods are the rod-shaped cells present in the retina of an eye which are sensitive to
dim light. (2)cones are the cone-shaped cells present in the retina of an eye which are
sensitive to bright light.
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20. Rangeof vision of a normal human eye
• the farthest point from the eye at which an object can be seen clearly is known as the
“far Point” of the eye. The far point of a normal human eye is at infinity
• Thee nearest point up to which the eye can see an object clearly without any strain is
called the “near point” of the eye.
• The near point of a normal human eye is at a distance of 25 centimetre from the eye
• The ciliary muscles of the eye can change the thickness of the soft and flexible eye lens
and change its coverging powder of eye lens
21. Lawsof reflectionof light
• *Laws of reflection of light*
• The reflection of light from a plane mirror takes place according to two laws which are known as laws of reflection of light.
• The laws of reflection of light are as follows:-
• 1st law:- The incident ray,reflected ray and the normal lies on the same plane.
• 2nd law:- The angle of incident is always equal to the angle of reflection.
•
• Problem:- An incident ray makes an angle of 35° with the surface of a plane mirror. What is the angle of reflection?
• Ans: Angle of incidence=90°-35°=55°
• Angle of incidence=angle of reflection=55°
• So,the angle of reflection is 55°.
23. Multiple images
Formula to find the number of images formed by mirror:360°/X – 1
Problem: calculate the number of images formed when two plane mirrors are inclined at angle of:
I)90°
II)120°
Answer: I) Number of images formed=360°/90°- 1
=4-1
=3
II)Number of images formed=360°/120°- 1
=3-1
=2
I
24. Visuallychallenged personcan read and write
Those persons who are “ unable to see “ are known as visually challenged persons.
The most popular resource for visually challenged person in which can make them read and write is Braille.
*What is a Braille?*
Braille is a written language for the visually challenged person in which characters (letters and numbers,etc) a
represented by patterns of raised dots.
The Braille was developed by Louis Braille who was himself a visually challenged person.
There is a Braille code for common languages mathematics and scientific notation.
There are many visually challenged person in the world who have great achievements to their credit. Helen
Keller, an American lecturer and author is perhaps the most famous and inspiring visually challenged person of
the world. Helen Keller lost her eyesight when she was only 18 months old. But because of her resolve and
courage she studied up to graduation in a University and wrote a number of books, including “The Story of My
Life”.
26. Careof oureye
Some of the precaution to protect our eyes and maintain healthy eyesight are as follows:
I) Wash your eyes at least why said day with clean water.
II) Do not read or write in dim light because it would stain on your eyes and may cause headache.
III) We should never look directly at the sun or other powerful light.
IV) Do not read by bringing the book to close to your eyes or by keeping it too far from the eyes.
V) Do not raw the eyes with hands to prevent injury to the eyes.
VI) If you find difficulty in reading a book or writing on the blackboard or you have to squeeze your eyes
to see clearly get your eyes checked by an eye specialist doctor immediately.
VII) In case of an injury or any other problem to the eyes consult an eye specialist doctor self treatment
can be dangerous to the eyes.etc
27. Defectsof theeyeand treatment
• There are three common eye defects, and they are(i) myopia or near-sightedness, (ii)
Hypermetropia or far sightedness
• These defects are corrected by the use of suitable spherical lenses.
28. • *Answer the following questions*
• Q.1) Define the incident ray
• Q.2) Define angle of reflection.
• Q.3) State the two laws of reflection.
• Q.4) Express the mathematical formula to calculate the number of images formed when
two mirrors are inclined at (x)angle.
• Q.5) How is hypermetropia corrected?
• Q.6) How is myopia corrected
29. Fill in the blanks
• 1)The line drawn perpendicular to surface of the mirror at the point of incidence is termed as the
____________.
• 2)The angle of incidence is ________to the angle of reflection.
• 3)The exposed surface of the eyeball has a transparent covering called _________.
• 4)__________ is also called nearsightedness and shortsightedness.
• Answer:
• 1)Normal
• 2)Equal
• 3)Cornea
• 4) Myopia
