The human eye structure contains several key parts that allow us to see the colorful world around us. The cornea allows light to enter the eye and the iris controls the size of the pupil to regulate light levels. The retina is where images are formed and contains rod and cone cells that detect light intensity and color. The lens, with help from ciliary muscles, focuses images onto the retina for clear vision at various distances. Common eye defects like myopia and hypermetropia result from issues with the lens and shape of the eyeball.

1. Class 10 Physics :
HUMAN EYE AND THE
COLORFUL WORLD

2. 48-megapixel
576 megapixels

3. Structure of a Human Eye

6. Part of eye Definition Function
Cornea Transparent and bulget out
spherical membrane
covering the front of the eye
Lights enters the eye through it
Iris Dark and muscular
diaphragm between the
cornea and the lens.
Controls the size of the pupil
Color of iris is what we call color of the eye
Pupil Small hole between the iris Modulates amount of light that enter the
eyes. In dim light it opens up completely
and in bright light it becomes small.
Ciliary Muscles Flexible muscles that hold
the lens in positions
Modifies the curvature of the eye lens to
see both distant and nearby objects
clearly

7. Part of eye Definition Function
Retina Light sensitive surface of the
eye on which the image is
formed.
Image of the object is formed here. It
connected with optic nerves that send
signals to brain
Cells of Retina
Rod Cells >Cone Cells
Cells present in the retina of
human eye
● Rod Cells - Respond to intensity of
light
● Cone cells - Respond to the
illumination (primary colors)
Aqueous
Humour
Liquid between cornea and
eye lens
● Helps the refracted light to be
focused on retina.
● Protects the eyes.
Vitreous
Humour
Jelly like fluid between eye
lens and retina
● Maintains the shape of the eye balls.
● Prevents it from collapsing.

8. ………… is the Transparent and
bulget out spherical
membrane covering the front
of the eye
A. IRIS
B. PUPIL
D. CORNEA
C. RETINA

9. Power of Accommodation
The ability of eye lens to focus on both nearby
and distant objects by adjusting the focal
length is known as the accommodation power.
Agent - With the help of ciliary muscles

12. But of course there is a limit to the
accommodation of human eye. That’s
why we have :
Near Point : Minimum distance at which
an object can be seen most distinctly
without any strain.
For a normal eye of an adult, it is 25 cms
Far Point : Farthest point up to which the
eye can see clearly. It is infinity to the
normal eye.

13. The near point of a hypermetropic eye is 1
m. What is the power of lens required to
correct this defect? Assume that the near
point of normal eye is 25cm.

14. Why do human beings have and need
to two eyes instead of just one?
It serves following functions :
● Better horizontal field view of 180
degrees instead of 150 degrees with
one eye.
● Ability to detect faint objects.
● Because our eyes are separated by a
few centimetres, each eye sees a
slightly different image. Our brain
combines the two images into one,
using the extra information to tell us
how close or far away things are.
● With 2 eyes we can have three
dimensional view of the world with
depth instead of a 2D view with just one
eye.

15. Defects in Human Eye

16. Myopia or Nearsightedness
In myopia, a person can see nearby objects
clearly but cannot see objects that are far.
Reasons :
● Excessive Curvature of the eye lens
● Elongation of the eyeball
In Myopia, image of the object is formed before
retina.

18. Hypermetropia or farsightedness
In hypermetropia, a person can see distant
objects clearly but cannot see objects that are
near to her.
Reasons :
● Focal length of eye lens too large
● Shortness of the eyeball
In Myopia, image of the object is formed after
the retina.

20. Presbyopia
It mostly happens in old people as near point
gradually recedes away with age.
Reasons :
● Weakness of ciliary muscles
● Hardening or loss of elasticity of lens
Sometimes a person has both myopia and
hypermetropia, in that case they are provided
with bifocal glasses.

21. Cataract :
Cataract happens when eye lens becomes milky
or cloudy due to the growth of a membrane over
it.
● It generally happens in old age
● Leads to partial or complete loss of vision
● Cataract can be corrected with a surgery

22. What would have been the
horizontal field of view for
humans if they had one
eye instead of two?
A. 150 degrees
B. 160 degrees
D. 360 degrees
C. 180 degrees

23. Refraction of Light Through a Prism

24. A prism is a transparent and refracting
medium with at least 2 lateral surfaces, 2
triangular bases, and 3 rectangular lateral
surfaces.
Angle between 2 lateral surfaces is known
as Angle of Prism.

25. Angle of deviation: is the angle which the emergent ray (extended
backwards) makes with the incident ray (extended forward).

26. Dispersion : Splitting of white light
into its constituent colors is called as
its dispersion.
White light is made up of 7 colors.
Please note : Dispersion doesn't take place
through every medium, some special mediums
known as dispersive mediums are there. Prism
is one of them
Dispersion of White Light Through Prism

27. Isaac Newton was
the first one to
obtain the
spectrum of light
using a glass
prism.

28. Light rays of different colors have different wavelengths
and they travel with same speed in vacuum and air, but
they travel with different in any other medium (like prism).
● Since they travel with different speeds, they are also
bent at different angles.
● Red light has the maximum wavelength and travels
faster. So it deviates the least
● Violet light has the minimum wavelength and travels
slowest. So it deviates the most.

30. RAINBOW IN SKY
A rainbow is a natural spectrum appearing
in sky after a rain shower.
It happens when the white light (sunlight)
is dispersed by the tiny water droplets
after rain that act as as individual prisms.
Same phenomenon is observed by looking
at the sky through a waterfall or through a
water fountain with the sun behind us.

32. A. A is true but R is false
B. A is false but R is true
D. Both A and R are true but R is not the
correct explanation of A
C. Both A and R are true and R is the correct
explanation of A
Assertion: The light of violet color deviates the
most and the light of red color the least while
passing through a prism
Reason: For a prism material, refractive index
is highest for red light and lowest for violet
light.

33. Atmospheric Refraction
Why does it happen :
It happens because atmosphere is not
uniform throughout, its density goes on
changing as we move up or down in
atmosphere
It is basically has layers of different
densities that are rarer/denser with respect
to each other.
Due to this, when light passes through
earth’s atmosphere, it undergoes
continuous refraction

35. Twinkling of Stars

37. Why don’t planets twinkle?
Stars are farther to earth’s surface while most
planets are closer to us. Due to this disparity in
distance, stars appear as tiny dot in the sky
while planets appear bigger, like a collection of
million dots.
In planets, each of these tiny individual dots do
twinkle just like stars do, but their overall effect
is cancelled out since when some dots are
brighter, others are dimmer. Thus, the net
twinkling effect is zero.

38. ADVANCED SUNRISE AND
DELAYED SUNSETS

41. Why do planets don’t
twinkle like stars do?
A. Planets are farther to us than
stars
B. Planets are closer to us than
stars
D. Both A and C
C. Planets don’t emit any light

42. Scattering of Light and
Tyndall effect

43. Scattering of Light
When a light beam goes through a medium, it
hits the particles existing in them.
Due to this phenomenon, some of the light
rays get absorbed while a few get scattered in
various directions. The intensity of the
scattered light rays depends on the particles’
size and wavelength.

44. TYNDALL EFFECT
The phenomenon
of scattering of
light by the
colloidal particles
gives rise to
Tyndall effect
This phenomenon is seen when a fine beam of
sunlight enters a smoke-filled room through a
small hole. Thus, scattering of light makes the
particles visible. 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.

45. Tyndall effect can also be observed when
sunlight passes through a canopy of a dense
forest. Here, tiny water droplets in the mist
scatter light.

46. According to Rayleigh's law for scattering
The amount of scattering of the light is inversely
proportional to the fourth power of the
wavelength.

47. Why is the colour of the clear Sky Blue?
The molecules of air and other fine particles in
the atmosphere have size smaller than the
wavelength of visible light. These are more
effective in scattering light of shorter
wavelengths at the blue end than light of
longer wavelengths at the red end.

48. What color the sky be if there wasn’t any
atmosphere?
If the earth had no atmosphere, there would
not have been any scattering. Then, the sky
would have looked dark. The sky appears
dark to passengers flying at very high
altitudes, as scattering is not prominent at
such heights

50. Colour of the Sun at
Sunrise and Sunset