The document discusses various parts of the human eye including the cornea, iris, pupil, lens, ciliary muscles, retina, vitreous humour, and blind spot. It describes the power of accommodation and how the eye focuses on near and far objects. Common vision defects like myopia, hypermetropia, and presbyopia are explained along with their corrections using lenses. The document also discusses dispersion and scattering of light through the atmosphere and prisms, including causes of rainbows, twinkling stars, and the blue color of the sky.

2. LearningObjectives
The Human Eye
The Important Parts of The Eye
Power of Accommodation
Defects of vision and their correction
Myopia or Near-sightedness, Hypermetropia or
Farsightedness, Presbyopia
Dispersion of light
 Scattering of light

3. TheImportant PartsofTheEye
Cornea: The front part of the eye is covered by transparent spherical
membrane called cornea.
Cornea

4. TheImportant PartsofTheEye
Iris: Just behind the cornea is a dark coloured muscular diaphragm
which has a small circular opening in the middle.
Cornea
Iris

5. TheImportant PartsofTheEye
Pupil: Pupil is the small circular opening of iris. The pupil appears
black because no light is reflected from it.
Cornea
Pupil
Iris

6. TheImportant PartsofTheEye
Eye Lens: The eye lens is a convex lens made of a transparent jelly -
like proteinaceous material.
Cornea
Pupil
Iris
Eye Lens

7. TheImportant PartsofTheEye
Ciliary muscles: The eye lens is held in position by ciliary muscles.
The ciliary muscles help in changing the curvature and focal length of
the eye lens.
Ciliary muscles
Cornea
Pupil
Iris
Eye Lens

8. TheImportant PartsofTheEye
Retina: The inner back surface of the eye ball is called retina. It is a
semi-transparent membrane which is light sensitive and is equivalent to
the screen of a camera.
Ciliary muscles
Cornea
Pupil
Iris
Eye Lens Retina

9. TheImportant PartsofTheEye
Vitreous humour: The space between the retina and eye lens is filled
with another fluid called vitreous humour.
Ciliary muscles
Cornea
Pupil
Iris
Eye Lens Retina
Vitreous humour

10. TheImportant PartsofTheEye
Blind Spot: It is a spot at which the optic nerve enters the eye and is
insensitive to light and hence the name.
Cornea
Iris
Pupil
Ciliary muscles
Eye Lens Retina
Vitreous humour
Blind spot
Optic Nerve

11. Power of Accommodation
Power of Accommodation: The ability of the eye to focus on
objects lying at different distances is called the power of
accommodation of the eye.
Near object
Far object

12. When the ciliary muscles are
relaxed, the eye lens becomes
thin. Thus, its focal length
increases and we see the distant
objects clearly.
When the ciliary muscles are
contract, then the curvature of
the eye lens is increases and the
eye lens becomes thick. Thus, its
focal length decreases and we
see the nearby objects.
Ciliary muscles
Thin Eye Lens
Thick Eye Lens
Power of Accommodation

13. Near point or least distance of
distinct vision is the point nearest
to the eye at which an object is
visible distinctly.
Far Point of The Eye
Far point of the eye is the
maximum distance up to which
the normal eye can see things
clearly. It is infinity for a normal eye.
Near Point of the Eye
25 cm
Power of Accommodation

14. Defects of Vision and Their Correction
• Myopia or near-sightedness
• Hypermetropia or far-sightedness
• Presbyopia
• Cataract

15. Myopia or Near-sightedness
Myopia :The light from a
distant object arriving at
the eye lens may get
converged at a point in
front of the retina in the
vitreous body.
Correction for myopia:
To compensate this, we
interpose a concave lens
between the eye and the
object, with the diverging
effect desired to get the
image focused on the
retina.
Myopic Eye
Correction
Concave Lens

16. Hypermetropia or Farsightedness
Hypermetropia: If the
eye-lens focuses the
incoming light at a point
behind the retina, this
defect is called far
sightedness or
hypermetropia.
Correction for
hypermetropic eye: A
convergent lens(convex
lens) is needed to
compensate for the defect
in vision.
Correction
Hypermetropic Eye
Convex Lens

17. Presbyopia
Presbyopia is a common type of vision disorder that occurs as you
age. It is often referred to as the aging eye condition. Presbyopia
results in the inability to focus up close, a problem associated with
refraction in the eye.

18. Cataract
Cataract: The crystalline lens of people at old age becomes milky and
cloudy. This condition is called cataract. This causes partial or
complete loss of vision. It is possible to restore vision through a
cataract surgery.
Milky and Cloudy Eye

19. Refraction of light through a glass prism

20. Refraction of light through a glass prism
Incident ray
Refracted ray
When a ray of light passes through a glass prism, it gets
bent twice at the air-glass interface and glass-air interface.
The emergent ray is deviated by an angle to the incident
Ray. This angle is called the angle of deviation.
Emergent ray
D
i
r
Air Glass Glass Air
Glass prism
e Angle of emergence
Angle of deviation
Normal

21. Dispersion of white light by a glass prism
Beam of white light
Spectrum
R
O
Y
G
B
I
V
When a beam of white light passes through a glass prism, it
is split into a band of colors called a spectrum.
This is called the dispersion of white light. The spectrum of
white has the colors violet, indigo, blue, green, yellow,
orange, and red (VIBGYOR). The red light bends the least and
the violet light bends the most.
Glass prism

22. Dispersion of white light by a glass prism:-

23. Recombination of the spectrum of white light
produces white light:-
R
V
V
R R
V
White light
White light
When a beam of white light passes through a glass prism, it
is split into its component colors. When these colors are
allowed to fall on an inverted glass prism it recombines to
produce white light.
Glass prisms

24. Rainbow formation
Raindrop
Violet
Sunlight
Refraction and dispersion
Internal reflection
Observer
Refraction
Red

25. Rainbow formation

26. Atmospheric refraction :-
Apparent position
Eye
Star
Real position
Increasing
refractive index
of atmosphere

27. Twinkling of stars
The twinkling of stars is due to the atmospheric refraction
of star light and due to the changing in the position of the
stars and the movement of the layers of the atmosphere.
So the light from the stars is sometimes brighter and
sometimes fainter and it appears to twinkle.
Planets are closer to the earth than stars. The light from
stars are considered as point source of light and the light
from planets are considered as extended source of light.
So the light from the planets nullify the twinkling effect.

28. Advance sunrise and delayed sunset:-
Earth
Observer
Sunrise
Sunset
Apparent position
Apparent position
Atmosphere
The sun is visible to us about 2 minutes before sunrise
and about two minutes after sunset due to atmospheric
refraction.
The apparent flattening of the sun’s disc at sunrise and
at sunset is also due to atmospheric refraction.
Horizon Horizon
Real position Real position

29. Scattering of light :-
i) Tyndall effect :-
When a beam of light passes through a colloidal solution, the path
of light becomes visible due to the scattering of light by the colloid
particles. This is known as Tyndall effect.
The earth’s atmosphere contains air molecules, water droplets, dust,
smoke etc. When sunlight passes through the atmosphere the path of
the light becomes visible due to the scattering of light by these
particles.
The colour of the scattered light depends upon the size of the
scattering particles. Very fine particles scatter blue light. Larger
particles scatter different colours of light.

30. 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.

31. Why is the colour of the clear sky blue?

32. Colour of the sky at sunrise and sunset :
At sunrise and at sunset the sun is near the horizon and
the light from the sun travels through the thicker layers of
the atmosphere and longer distance through the
atmosphere. Near the horizon most of the blue light and
shorter wave lengths are scattered away by the particles of
the air and the red light and longer wave lengths reaches
our eyes. So the sun appears reddish at sunrise and sunset.
Observer
Sun overhead
Blue light scattered away
Sun appears reddish
Sun near horizon
Atmosphere
Earth

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