wonderful explanation of the topic human eye and the colorful world

1. MADE BY :- SHRISH OJHAMADE BY :- SHRISH OJHA
andand
ARYAMAN SINGH MARJARAARYAMAN SINGH MARJARA

2. 1. The Human Eye.
2. The Parts and Functions of a Human Eye.
3. Power of Accommodation and LDDV
4. Defects of Vision and their Correction -
Myopia, Hypermetropia and Presbyopia.
5. Refraction through a Prism.
6. Expression for Refractive Index of Prism.
7. Dispersion .
8. Rainbow.
9. Atmospheric Refraction – Tyndall Effect, Apparent position &
Twinkling of Stars, Delayed Sunrise & Sunset.
10.Scattering of Light - Blue Colour of the Sky and Red Colour of
the Sun.

3. Internal structure of Human Eye

4. CRYSTALLINE LENCE
AQUEOUS HUMOURAQUEOUS HUMOUR
PUPILPUPIL
IRISIRIS
CORNEACORNEA
VITREOUS HUMOURVITREOUS HUMOUR
OPTIC NERVEOPTIC NERVE
RATINARATINA
CILIARY MUSCLESCILIARY MUSCLES

5. •The crystalline lens is a lens which merely provides
the finer adjustment of focal length required to focus
objects at different distances on the ratina.

6. It is a watery fluid between corneaIt is a watery fluid between cornea
and lensand lens

7. It is a gap between iris whichIt is a gap between iris which
ensure the amount of light enteringensure the amount of light entering
the eyethe eye

8. •Iris is a dark muscular diaphragm behind the cornea and it controls the
size of the pupil.
• The pupil regulates and controls the amount of light entering the eye.

9. Cornea is a thin membrane which forms the transparent bulge on the
front surface of the eye ball.
Light enters in the eye through it.
Most of the refraction of light rays entering the eye occurs at the outer
surface of the cornea.

10. It is a oily fluid lens and retinaIt is a oily fluid lens and retina

11. The nerve which carry theThe nerve which carry the
information regarding the image toinformation regarding the image to
the brainthe brain

12. Image is formed on a light-sensitive screen called the retina.
The eye lens forms an inverted real image of the object on the retina.

13. These are the muscles which contract or expand to makeThese are the muscles which contract or expand to make
the focal length of the lens to increase or decrease.the focal length of the lens to increase or decrease.

14. Power of Accommodation
The ability of the eye lens to adjust its focal length is called
accommodation.
The eye lens is composed of a fibrous, jelly-like material
and its curvature can be modified by the ciliary muscles.
Hence, the focal length can be changed as per the
requirement. This enables us to see the distant or near by
objects clearly.

15. Least Distance of Distinct Vision
(LDDV):
The minimum distance, at which objects
can be seen most distinctly without strain,
is called Least Distance of Distinct
Vision(LDDV). For a normal eye, LDDV is
25 cm.

17. Myopia or Short-sightedness or Near-
sightedness
A person with myopic eye can see nearby objects clearly but cannot
see distant objects distinctly.
Such a person may clearly see upto a distance of a few metres.
In myopic eye, the image of a distant object is formed in front of the
retina and not on the retinal itself.
This defect may arise due to
(i) excessive curvature of the eye lens (short focal length of the eye
lens)
or
(ii) Elongation of the eyeball.
Myopia can be corrected by using a concave lens of
suitable power(focalpower(focal length).

18. LDDV = 25 cm
O
LDDV = 25 cm
I
O
LDDV = 25 cm
Myopic Eye
O
I
I
O
LDDV = 25 cm
I
O
LDDV = 25 cm
II
Near Point
Myopic Eye corrected with Concave Lens
Normal Eye

19. Hypermetropia or Long-sightedness or
Far-sightedness
A person with hypermetropia can see distant objects clearly but cannot
see nearby objects distinctly.
Such a person may has to keep a reading material much beyond 25 cm
from the eye for comfortable reading.
In hypermetropic eye, the image of a nearby object is formed behind the
retina and not on the retinal itself.
This defect may arise due to
(i) long focal length of the eye lens or
(ii) Very small size of the eyeball.
Hypermetropia can be corrected by using a convex lens of
suitable power (focal length).

20. LDDV = 25 cm
Hypermetropic Eye
O
Near Point
LDDV = 25 cm
I
O
O
LDDV = 25 cm
I
I
LDDV = 25 cm
I
O
LDDV = 25 cm
O
II
Hypermetropic Eye corrected with Convex Lens
Normal Eye

21. Presbyopia
The power of accommodation of the eye usually decreases with ageing.
People can not see nearby objects comfortably and distinctly without
corrective eye-glasses.
This defect is called presbyopia.
It arises due to
(i) gradual weakening of the ciliary muscles and
(ii) diminishing flexibility of the eye lens.
Sometimes, a person may suffer from both myopia and hypermetropia. Such
people require bi-focal lenses which consists of both concave and convex
lenses. The upper portion is concave for distant vision and the lower portion
is convex for near vision.

23. N1
N2
Eye
A
Refracting Surfaces
Prism
i
e
REFRACTION OF LIGHT BY A TRIANGULAR
PRISM
Q
P
S
R

24. Refraction of Light through Prism:
A
Refracting Surfaces
Prism
i
A
B C
e
Or1 r2
N1 N2
μ
Q
P S
R

25. DISPERSION OF WHITE LIGHT THROUGH A PRISM
The phenomenon of splitting a ray of white light into its constituent colours
(wavelengths) is called dispersion and the band of colours from violet to red
is called spectrum (VIBGYOR).
A
B C
D
White
light
R
O
Y
G
B
I
V
Screen
N

26. A
B C
White
light
N
A
B’ C’ White
light
Recombination of spectrum of white light:

27. A rainbow is a natural spectrum which is caused
by dispersion of sunlight by tiny water droplets
present in the atmosphere after a rain shower.
The incident sunlight with suitable angle of
incidence is refracted, dispersed, and finally
refracted out by the rain drops.
Due to the dispersion and internal reflection,
different colours reach the eye of the observer.
RAINBOW

28. Eye
41º
43º
Sunlight
Rain drop
Formation of Rainbow
A line parallel to Sun’s ray

29. ATMOSPHERIC REFRACTION
Flickering of objects above a fire:
The apparent random wavering or flickering of objects can be seen through
a turbulent stream of hot air rising above a fire.
The air just above the fire becomes hotter than the further up. The hotter air
is lighter than the cooler air above it, and has a refractive index slightly less
than that of the cooler air.
Since the physical conditions of the refracting medium (air) are not
stationary, the apparent position of the object, as seen through the hot air,
fluctuates. This wavering is therefore due to an effect of atmospheric
refraction on a small scale in the local environment.
Refraction of light by earth’s atmosphere is called atmospheric refraction.

30. Twinkling of Stars:
The twinkling of a star is due to atmospheric refraction
of starlight.
The atmospheric refraction occurs in a medium of
gradually changing refractive index.
Since the atmosphere bends starlight towards the
normal, the apparent position of the star is slightly
different from its actual position.
The star appears slightly higher (above) than its actual
position when viewed near the horizon.
This apparent position is not stationary, but keeps on
changing slightly, since the physical conditions of the
earth’s atmosphere are not stationary.
Since the stars are very distant, they approximate point-
sized sources of light.
As the path of rays of light coming from the star goes
on varying slightly, the apparent position of the star
fluctuates and the amount of light entering the eye
flickers- the star sometimes appear brighter, and at
some other time, fainter which gives the twinkling
effect.
Eye
DensityofAtmosphere&
Refractiveindexincrease
Apparent position
of the Star
Real
position
of the
Star

31. SCATTERING OF LIGHT
Tyndall Effect:
The earth’s atmosphere is a heterogeneous mixture of minute particles.
These particles include smoke, tiny water droplets, suspended particles of
dust and molecules of air.
When a beam of light strikes such fine particles, the path of the beam
becomes visible.
The light reaches us, after being reflected diffusedly by these particles.
The phenomenon of scattering of light by the colloidal particles gives rise to
Tyndall Effect.
Tyndall Effect can be seen when a fine beam of sunlight enters a smoke-filled
room through a small hole. In this, scattering of light makes the particles
visible.
It can also be seen when sunlight passes through a canopy of a dense forest.
In this, tiny water droplets in the mist scatter light.
The colour of the scattered light depends on the size of the scattering
particles.
Very fine particles scatter mainly blue light while particles of larger size
scatter light of longer wavelengths. If the size of the scattering particles is
large enough, then, the scattered light may even appear white.

32. SCATTERING OF LIGHT
- Activity
S
L1 ScreenL2
I
Sodium thio sulphate
solution (hypo)
Conc. Sulphuric acid

33. ii) Why is the colour of the clear sky blue ?
The fine particles in the atmosphere have size smaller than the
wave length of visible light. They can scatter blue light which has a
shorter wave length than red light which has a longer wave length.
When sunlight passes through the atmosphere, the fine particles in
the atmosphere scatter the blue colour more strongly than the red
and so the sky appears blue.
If the earth had no atmosphere there would not be any scattering
of light and the sky would appear dark. The sky appears dark at very
high altitudes.