explanation about human eye

1. NAVODAYA VIDYALAYA SAMITI, NOIDA
e-content for class X
Chapter 11
Human eye and Colourful World
Prepared by
Sreeja K S , JNV Mandya
Karnataka.

2. HUMAN EYE AND COLOURFUL WOLD
Focus Points:

3. Human Eye

4. Parts of eye and their functions
Part Definition Function
Cornea Transparent membrane on
the front portion of the eyeball
Light enters the eye
Iris opaque circular diaphragm Controls the size of the
pupil
Pupil Small central hole in the iris It regulates and controls
the amount of light
entering the eye
Vitreous
humour
Jelly like fluid between retina
and eyelens
It helps to maintainits
shape and overall eye
health
Optic
nerve
Nerve which connects eye
and brain
Carries the electrical
signal to the brain

5. Parts of eye and their functions
Part Definition Function
Ciliary
muscles
The small muscle that permits
the lens to change its shape in
order to focus near or distant
objects
Changes the shape of the
eye lens and its focal
length
Eyelens A biconvex lens composed of
fibrous, jelly-like material
Focus the images of
objects on retina
Retina Light sensitive membrane on
the backwall of the eyeball
Images are formed and
transmitted to the brain
Aqueous
humour
Salty fluid between cornea and
eyelens
It gives the eye its shape
nourishes the cornea and
lens by supplying nutrition

6. Terms related to eye
• Accommodation: Ability of eye lens to change the focal
length to form image on the retina.
• Least distance of distinct vision(Near point): The
minimum ditance from the eye, at which the eye can see
the objects clearly and distinctly without any strain.
• For a normal eye, its value is 25 cm
• Far point: The farthest point from the eye, at which an
object can be seen clearly by the eye .
• For a normal eye, the far point is at infinity.

7. 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

8. Defects of vision and their correction
Defect Cause correction
Myopia(Near
sightedness)
Large eyeball, small focal
length of eye lens
Concave
lens
Hypermetropia(Lo
ng sightedness)
Small eyeball, Large focal
length of eye lens
Convex
lens
Presbyopia Accommodating power of
eye lens decreases due to
stiffening of eye lens
Convex
lens

9. Ray dagram of hypermetropia and myopia

12. Recombination of seven colours to
form white light

13. Formation of rainbow
It is a beautiful spectrum of light produced
by refraction, dispersion and internal
reflection of sunlight by spherical raindrops

14. Atmospheric refraction
Twinkling of stars:
This apparent position is not stationary but keeps on changing
due to the change in atmospheric conditions like density,
temperature etc.
The path of the rays of light coming from the star goes on
varying sightly.
The amount of light entering our eyes from a particular star
increases or decreases randomly with time.

15. Atmospheric refraction
The planets do not show twinkling effect:
The planets are much closer to the earth.
Tthe amount of light received from them is much
greater.

16. Advance sunrise and delayed sunset
 The sun is visible about two minutes before actual sunrise and
about two minutes after actual sunset,because of atmospheric
refraction.
 With altitude, the density and hence refractive index of air-layer
decreases.
 The light rays starting from the sun travel from rarer to denser
layers.
 They bend more and more towards the normal.
 To an observer on the earth, light rays appears to
come from position above the horizon.
 The sun which is actually in position below the
horizon, appears to position above the horizon.

17. Scattering of light
 The blue colour of the sky is due to the scattering of the sunlight
by the molecules of the atmosphere.
 The molecules of air have sizes smaller than the wavelength of
visible light.
 They scatter blue light of shorter wavelength more strongly than
red of longer wavelength.
 The scattered light enters the eye and the sky appears blue.

18. Scattering of light
• Reddishness of the sun at sunrise and sunset:
The shorter wavelength blue light is scattered
away from the observer and the long wavelength
red light, which is least scattered reaches the
observer.

19. Scattering of light
• Red colour of danger signal:
Because of the longer wavelength,
red is least scattered and can reach
far distance.

20. Links for further information:
https://www.vedantu.com/ncert-solutions/ncert-solutions-class-
10-science-chapter-11-human-eye-and-colourful-world
https://epathshala.nic.in/topic.php?id=1064
https://avanti.in/human-eye-colorful-world-class-10/
https://physicscatalyst.com/Class10/human_eye_colourful_world
_important_questions-1.php
https://www.topperlearning.com/ncert-solutions/cbse-class-10-
physics/ncert-physics-x/human-eye-and-the-colourful-world
https://www.vidyakul.com/cbse-class-10-science-notes-chapter-
11-human-eye-and-colourful-world/