UNDERSTANDIUNDERSTANDING NG

REFRACTIONREFRACTIONThe change in the The change in the direction of light direction of light when it passes when it passes from a one from a one transparent transparent medium to medium to another is called another is called refraction..refraction..

Refraction of light when light travels from air into water. Lets understand the phenomena of reflection. Then light travels from a rare medium air into denser medium water. Study the diagram shown here. AB is the surface seprating air from water. The ray of light falling on the surface is called incident ray. The angle between the incident ray and the normal is called the angle of incident (i). The ray which has change its direction is called the refracted ray. The angle between the refracted ray and the normal is called the angle of refraction (r).

The parts of human eye is described as below:-

1. Sclerotic:- It is the outer layer which protect us from external injuries.2. Cornea:- through cornea the light entered into eye.3. Choroid :- It is the second layer which lies below the sclerotic. It is black

from inside so that light is not scattered.4. Iris:-Iris colour is black or brown. In the center of iris a small hole is present

called pupil..Pupil size is insreces or decreces. It depends upon the intensity of light.

5. Eye Lens:-A double convex lens is present in eye with the help of this lens images is formed on the retina.

6. Ciliary Muscles:- Ciliary muscles hold the lens in position.7. Pupil:- It is hole in the center of iris.8. Aqueous Humour:- It is a fluid which is present between cornia and lens.9. Vitreous Homour:- It is jelly like fluid which is filled between lens and

retina. 10. Retina:- It is third layer which act as a screen on which the image is found.11. Optic Nerve:-It sends message to the brain.12. Eye lids:- It protect the eyes from dusT.

Short Sightedness:- In this defect we see the object from near clearly but not seen from far away object. This defect is occur due to decreses the focal length of lens. It is corrected by using concave lens.

Long Sightedness:-In this defect we see the distant object clearly. But not seen the object fron nearly. This defect is occur due to the increases the focal length of lens. This defect is corrected by using the convex lens.

There are two types of telescope:-1. Astronomical telescope:- With the help

this telescope we can see the stars ,planets and glaxies etc.

2. Terrestrial telescope:- with the help of this telescope we can see the objects on the earth.

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