HELLO EVERYONE MY NAME IS DAKSH GUPTA I READ IN CLASS 8 THIS PRESENTATION WILL HELP YOU TO MAKE YOUR OWN PRESENTATION BETTER THAN ME THANK YOU FOR SEEING THIS PRESENTATION
2. WHAT DO YOU UNDERSTAND THE
REFRACTION OF LIGHT ?
• This bending by refraction makes it possible for us to
have lenses, magnifying glasses, prisms and rainbows.
Even our eyes depend upon this bending of light.
Without refraction, we wouldn't be able to focus light
onto our retina.
4. REFRACTION OF LIGHT
• When a ray of light enters from one medium to
another, then it deviates from its actual path. This
phenomenon is called refraction of light.
5. REFRACTION AND THE SPEED OF LIGHT
• Light travels at lower speeds in glass and water than in air . We say that
glass and water are optically denser than air .
• Optical density :
• Optical density is a property of a transparent material. It is a measure of
the speed of light through the material.
6. • when a ray of light travels from a rarer medium to a denser medium, then it
bends towards the normal and when the light travels from a denser medium
to a rarer medium, it bends away from the normal.
7. • when a ray of light travels from a rarer medium to a denser medium, then it
bends towards the normal and when the light travels from a denser medium
to a rarer medium, it bends away from the normal.
8. EFFECTS OF REFRACTION
• Real and apparent depth :
• The real depth is the actual depth of the bottom of the tank and the
apparent depth is the virtual depth that is observed as a result of the
refraction of light. The apparent depth depends upon the refractive index of
the medium.
9. • Apparent bending of a pencil
• Rays of light from the tip of the pencil bend away from the normal as they go
from water to air. The refracted appear to come from point . Thus the immersed
portion of a pencil in water appears . Hence, the pencil appears to bent at the
water surface. Moreover, the immersed portion of the pencil in water also
appears to be shorter than the actual length of the pencil.
10. REFRACTION THROUGH THE GLASS SLAB
• Since the angle of incidence is equal to the angle of emergence, therefore
the emergent ray is parallel to the incident ray. In the glass slab, the light
ray gets refracted two times firstly, from rarer to denser medium and
secondly from denser to rarer medium
11. REFRACTION THROUGH A PRISM
• Refraction is the bending of light when it goes from one medium to
another so, when a ray of light passes through a glass prism, refraction of
light occurs both, when it enters the prism as well as when it leaves the
prism.
12. DISPERSION
• When white light is passed through a glass prism it splits into its spectrum
of colours (in order violet, indigo, blue, green, yellow, orange and red) and
this process of white light splitting into its constituent colours is termed as
dispersion.
13. REASON FOR DISPERSION OF LIGHT
• Cause of Dispersion: When white light passes through a glass
prism, its constituent colours (red, orange, yellow, green, blue,
indigo, violet) travel with different speeds in the prism because
refractive index is color dependent. This causes the dispersion
of light.
15. LENSES ARE CLASSIFIED INTO TWO TYPES :
CONCAVE LENS :A CONCAVE LENS IS THINNER IN THE MIDDLE AND THICKER
AT THE EDGES. IT IS ALSO KNOWN AS CONVERGING LENS
CONVEX LENS : A CONVEX LENS IS THICKER IN THE MIDDLE AND THINNER AT
THE EDGES. AS IT IS ALSO KNOWN AS DIVERGING LENS
16. • Principal axis. :
• An imaginary line passing through the centers of two spheres of which the
spherical lens is a part is known as the principal axis
TERMS RELATED TO LENSES
17. • Optical Centre:
• The point on a lens through which a ray of light passes without deviation is
called the optical centre of the lens.
TERMS RELATED TO LENSES
18. • Principal Focus:
• The point on a lens through which a ray of light passes without
deviation is called the optical centre of the lens.
TERMS RELATED TO LENSES
19. • Focus length :
• The distance between the focus and the optical center is known
as focal length. It is denoted by f.
TERMS RELATED TO LENSES
21. The image formed by a convex lens
varies in size, position and nature (erect
or inverted , real or virtual ) depending
upon the distance of the object from the
lens .
IMAGE FORMED BY A CONVEX LENS
22. • When an object is at infinity , then the rays coming from it is almost parallel to
principal axis. Hence the image formed is at focus.
• The image of a very far off object (object at infinity) is a real, diminished and
almost point-like image.
OBJECT VERY FAR OFF ( OR AT INFINITY):
23. • When an object is placed beyond 2f in front of a convex lens , then the image
formed is between f and 2f on the other side of the lens , it is real , inverted
and smaller than the object . It can be formed on a screen placed at that point
.
OBJECT BEYOND 2F :
24. • When an object is placed at 2f in front of a convex lens, the image is real,
inverted and and of the same size the object
OBJECT AT 2F :
25. • When an object is placed between F and 2F in front of a convex lens ,The
image is real , inverted and larger than the object . It is situated beyond 2f on
the other side of the lens
OBJECT BETWEEN F AND 2F
26. • When an object is placed at 2f in front of a convex lens, The image is real
, inverted and inverted . It is highly enlarged in size than the object . The
image is formed at infinity .
OBJECT AT F
27. •When an object is placed between F and 0 in front of a convex lens, then its
image is formed between C1 and F1. The image is enlarged, erect and virtual.
•
OBJECT BETWEEN F AND 0
28. A diverging lens always forms a virtual image , which is erect and smaller in
size than the object . It is formed between the optical centre and the focus,
on the same side of the lens as the object .
•
THE IMAGE FORMED BY A CONCAVE LENS
29. EYE – THE NATURAL OPTICAL INSTRUMENT
• Light entering the human eye is first refracted by the cornea. The refracted
light is then incident on an iris. The lens is just behind the iris and light
after refracted through the pupil falls on it and forms a sharp image. Image
formation exactly on the retina enables us to see the object real and
inverted.
30. • Functions of human eye ( the natural optical instrument )
• Cornea : The eye consists of the eyeball which is nearly spherical in
shape . It in front portion ,
• It is called cornea . The light enters the eye through the cornea
• Iris The colored tissue at the front of the eye that contains the pupil
in the center. The iris helps control the size of the pupil to let more
or less light into the eye.
• Pupil The pupil is the opening at the center of the iris through which
light passes. The iris adjusts the size of the pupil to control the
amount of light that enters the eye.
• Aqueous The aqueous humour is a thin, transparent fluid similar to
plasma. It's made up of 99.9% water – the other 0.1% consists of
sugars, vitamins, proteins and other nutrients. This fluid nourishes
the cornea and the lens, and gives the eye its shape
31. • Lens The image formed by the eye lens on the retina is real,
inverted, diminished.
• Retina The image formed at the retina of the human eye is real and
inverted. It is due to the presence of a convex lens in the eye.
• Ciliary muscles The ciliary body is a circular structure that is an extension of
the iris, the colored part of the eye. The ciliary body produces the fluid in
the eye called aqueous humor. It also contains the ciliary muscle,
which changes the shape of the lens when your eyes focus on a near objec
• Vitreous humour The vitreous humor's main role is to maintain the round
shape of the eye. The size and shape of the vitreous humor also ensures
that it remains attached to the retina, which is the layer at the back of the
eye that is sensitive to light
• Cone cones are sensitive to bright light, can detect colour . We have three
types of cones: blue, green, and red.
• Rods They are sensitive to light levels and help give us good vision in low
light. They are concentrated in the outer areas of the retina and give us
peripheral vision.
32.
33. BLIND SPOT – THE AREA OF NO VISION
• At the junction of the optic nerve and the retina, there are no sensory cells
that could produce impulses when light falls on that location, so no vision is
possible at that spot. This is called the blind spot.
34. ACCOMMODATION OF THE EYE
• The capacity of the eye lens to adapt its focal length throughout the order to
clearly concentrate rays from a distant and a close object here on the
retina is called the eye's accommodating power. Human eye lenses are
translucent and crystalline.
• The least distance at which the ye can see an object clearly is called the near
point of the ye . The far point of the eye is the
maximum distance at which it can see clearly. For a normal eye the near
point is about 25 cm and the far point of the eye is at infinity. A normal eye
can see objects clearly that are between 25 cm and infinity.
36. DEFECTS OF VISION
• There are two main defects the eye suffers from
• These are :
• Myopia
• Hypermetropia
37. DEFECTS OF VISION
Myopia : Myopia is an eye defect or common abnormality of the eye in which
the near vision is clear while distant vision is blurred. This condition is known
as myopia also it is called near or short-sightedness. Retina is that part of the
eye which provides a surface for image formation.
38. DEFECTS OF VISION
• The far point of a myopic
person is 80 cm in front of
the eye.
40. DEFECTS OF VISION
• Hypermetropia or long
sightedness .
• Hypermetropia is also known
as far-sightedness. A person
with hypermetropia can see
distant objects clearly but
cannot see nearby objects
distinctly. The near point, for
the person, is farther away
from the normal near point
(25 cm)
41. DEFECTS OF VISION
• Near point of hypermetropic
eye
• For a person suffering from
hypermetropia , the near
point is beyond 25 cm
42. DEFECTS OF VISION
• Defect corrected by convex
lens .Hypermetropia is
corrected using a convex lens
of appropriate power. The
convex lens converges the
light rays so that the final
image from human eye lens is
formed on the retina.
43. DEFECTS OF VISION
• Cataract :
• The medical condition in which
the lens of eye of a person
becomes progressively cloudy
resulting in blurred vision is
called cataract. Cataract
develops when the eye-lens of a
person becomes cloudy (or even
opaque) due to the formation of
a membrane over it.
44. CARE OF THE EYES
• We must take proper care of the eyes . We must try to avoid any
kind of injury to our eyes . Some simple precautions given below
may help in protecting our eyes .
• Do not work or read in a dim light or very bright light. This tires the
eyes
• wash our eyes regularly with cold water
• We must get eyesight checkups done in case of any changes in the
vision.
• We must avoid watching screens for a very long period of time.
• Etc.
45. PERSISTENCE OF VISION
• Even after the object is removed, the impression of an object
seen by the eye remains on the retina for 1/16th of a second.
If we see another object before this time, the impressions of
the two merge to give us a sense of continuity. This eye
property is known as persistence of vision.
46. Visually impairment is the decrease in the ability of a person's sight to a large degree
such that it cannot be fixed by any conventional means of corrections like glasses and
lenses. The term blind people or blindness refers to a complete or nearly complete vision
loss.
THE VISUALLY IMPAIRED
47. Use braille
Braille is a system developed by Louis Braille in 1824 to help visually challenged people. It
is a code by which languages such as English, French, Spanish, etc can be written and
read. This code consists of raised dots, that can be read with fingers by blind people.
THE VISUALLY IMPAIRED
