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1. The human eye is like a camera. Its lens system forms an image on a light sensitive screen called the retina.
2. The eye ball is approx. spherical in shape with a diameter of 2.3cm.
3. The human eye has the following parts:-
(a) Cornea:-The transparent spherical membrane covering the front of the eye.
(b) Iris:-The coloured diaphragm between the cornea and lens.
(c) Pupil:-The small hole in the iris.
(d) Eye lens:-Its is a transparent lens made of jelly like material.
(e) Ciliary muscles:-These muscles hold the lens in position.
(f) Retina:-The back surface of the eye.
(g) Blind spot:-The point at which the optic nerve leaves the eye. An image formed at this point is not
sent to the brain.
(h) Aqueous humour:-A clear liquid region between the cornea and the lens.
(i) Vitreous humour:-The space between eye lens and retina is is filled with another liquid called
Vitreous humour.
4. In the eye, the image is formed on the retina by successive refraction at the cornea, the aqueous
humor, the lens and the vitreous humuor.
Electrical signals then travel along the optic nerve to the
brain to be interpreted. In good light, the yellow spot is most sensitive to detail and the image
automatically formed there.
5. Accomodation:-The ability of the eye to focus both near and distant objects, by adjusting the focal
length, is called the accommodation of the eye or the ability of the ciliary muscles to change the focal
length of the eye lens is called accommodation.
6. Defects of the eye:- Although the eye is one of the most remarkable organs in the body, it may
have several abnormalities, which can often be corrected with eye glasses, contact lenses, or surgery.
The various defects from which an eye can suffer are
Electrical signals then travel along the optic nerve to the
brain to be interpreted. In good light, the yellow spot is most sensitive to detail and the image
automatically formed there.
5. Accomodation:-The ability of the eye to focus both near and distant objects, by adjusting the focal
length, is called the accommodation of the eye or the ability of the ciliary muscles to change the focal
length of the eye lens is called accommodation.
6. Defects of the eye:- Although the eye is one of the most remarkable organs in the body, it may
have several abnormalities, which can often be corrected with eye glasses, contact lenses, or surgery.
The various defects from which an eye can suffer are
(i) Hypermetropia or long sightedness. (ii) Myopia or short sightedness and (iii) *Astigmatism. (iv)
Presbyopia.
7. Hypermetropia, hyperopia or long sightedness:- A person suffering from this defect can see distant objects clearly but cannot see nearby objects clearly.
In this defect, the near point lies further away from 25cm.Hypermetropia (far sightedness- the image of nearby objects is focused beyond the retina) is corrected by using a convex lens of suitable power. The eye losses its power of accommodation at
old age.
8. Hypermetropia is due to the following reasons:-
(i) Either the hyperopic eye ball is too short or
(ii) The ciliary muscle is unable to change the shape of the lens enough to properly focus the image
that is the focal length of the eye lens increases.
9. Myopia or short sightedness or near sightedness:-A person suffering from myopia or short
sightedness can see nearby objects clearly but cannot see the faraway objects clearly. Myopia
(shortsightedness-the image of distant objects is focused before the retina) is corrected by using a
concave lens of suitable power.
10. Presbyopia is the defect of human eye due to which an old person cannot read and write
comfortably. That is why presbyopia is also called old sight.
Explaination of Astigmatism:- The defect by which the person is notable to differentiate horizontal
and vertical position, is called astigmatism. It can be rectified by using cylindrical lenses.
11. As our two eyes are separated by a few centimeters, each eye observes a slightly different image.
Our brain combines the two views into one and we get to know how close or far away the things seen
are.
12. The smallest distance, at which the eye can see objects clearly without strain, is called the near
point of the eye or the least distance distinct vision. For a young adult with normal vision, it is about
25cm.
13. The distance between far point and near point of the eye is called range of vision of the eye.
14. Spectrum is a band of distinct colours we obtain when white light is split by a prism.
15. Causes of dispersion:-Every colour has its own characteristic wave length or frequency. Different
colours move with same speed in air/vacuum. But their speeds in refracting media like glass are
different. Therefore, refractive index of the medium for different colours is different. As a result,
different colours undergo different deviations on passing through the prism. Hence, different colours
emerge from the prism along different directions.
16.In any medium other than air/vacuum red light travels the fastest and violet light travels the
slowest.
17. When we pass white light through two identical prisms held side by side with their refracting
edges in opposite direction; the first prism disperses white light into seven colours and the second
prism recombines the seven colours into white light. Thus light emerging from second prism is white.
18. A rainbow is formed due to dispersion of light by tiny droplets of water which act as prisms.
19. Scattering of light causes the blue colour of the sky and the reddening of the sun at sunrise and
sunset.
20.When the sun is overhead at noon, then the light coming from the sun has to travel a relatively
shorter distance through the atmosphere to reach us. As a result, only a little of the blue colour of the
white light is scattered (most of the blue light remains in it). Since the light coming from the
overhead sun has almost all its components colours in the right proportion, therefore, the sun appears
white.
21.Prism The transparent object made of glass having two triangular ends and three rectangular faces
kept at an angle is called prism.
22.Angle of prism The angle between the surfaces of the prism is called the angle of prism.
23.Angle of deviation The angle between the indcident ray and the emergent ray in the refraction
through prism is called angle of deviation.
24.Spectrum The band of seven different colours formed by splitting white light through a prism is
called prism. Red colour deviates least while violet colour deviates most because wavelength of red
colour is maximum while of violet colour is minimum.
26.Dispersion of light The phenomenon of splitting of white light into its component colours is called dispersion of light. It takes place because of the angles of refraction of light for different colours are different.
27. Formation of rainbow seen after a rain shower as the tiny droplets of water act as tiny prisms and
cause dispersion of sunlight. A rainbow always forms in the direction opposite to the sun. The
essential condition for observing a rainbow is that the observer must stand with his back towards the
sun.
28. Atmospheric refraction : The atmosphere has different layers of air having diffrent optical
densities. The refraction caused by theses layers of atmosphere is called atmospheric refraction.
29.Twinkling of stars : The light of stars undergoes refraction many times before reaching the
observer due to varying densities of different layers of atmosphere. So the light of stars reaching our
eye increases and decreases continuously and the stars appear twinkling.
30.Tyndall effect : The scattering of light by colloidal particles in their path is called Tyndall effect.
Tyndall discovered that when white light is passed through a clear liquid having small suspended
particles in it (colloidal solution), the blue colour of white light having shorter wavelength is
scattered much more than the red colour having larger wavelength.
Useful study link from: http://jsuniltutorial.weebly.com/the-human-eye-and-the-colourful-world.html
10th Human eye and Atmospheric refraction Notes
10th Human eye and Atmospheric refraction Notes
Human Eye & Atmospheric Refraction Solved paper -2
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