The Human Eye and the Colourful World Class 10 PPT

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THE HUMAN EYE                                                                                  
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THE HUMAN EYE                                                                                  1a) The human eye :-           The human eye is the sense organ which helps us to see the  colourful world around us.       The human eye is like a camera. Its lens system forms an image on a light sensitive screen called retina. The eye ball is almost spherical in shape with a diameter of about 2.3cm. Light enters the eye through a transparent membrane called cornea.  Behind the cornea is  a  muscular diaphragm called iris which has an opening called pupil. The pupil controls the amount of light entering the eye. The eye lens helps to focus the image of objects on the retina. The ciliary muscles helps to change the curvature of the lens and to change its focal length. b) Working of the eye :-      The eye lens forms a real inverted image of the object on the retina. The light sensitive cells in the retina then produce electrical signals which are carried by the optic nerves to the brain. The brain  processes the information and sends the message to the eye and then we  see the object. 
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THE HUMAN EYE                                                                                  1a) The human eye :-           The human eye is the sense organ which helps us to see the  colourful world around us.       The human eye is like a camera. Its lens system forms an image on a light sensitive screen called retina. The eye ball is almost spherical in shape with a diameter of about 2.3cm. Light enters the eye through a transparent membrane called cornea.  Behind the cornea is  a  muscular diaphragm called iris which has an opening called pupil. The pupil controls the amount of light entering the eye. The eye lens helps to focus the image of objects on the retina. The ciliary muscles helps to change the curvature of the lens and to change its focal length. b) Working of the eye :-      The eye lens forms a real inverted image of the object on the retina. The light sensitive cells in the retina then produce electrical signals which are carried by the optic nerves to the brain. The brain  processes the information and sends the message to the eye and then we  see the object. c) Power of accomodation of the eye :-     The ability of the eye lens to see both near and distant objects by adjusting  its focal length is called the power of accommodation of the eye.    The eye lens is composed of a fibrous jelly like material. Its curvature can be changed to some extent by the ciliary muscles. The change in the curvature of the eye lens can change its focal length. When the muscles are relaxed, the lens becomes thin and its focal length increases and when the muscles contract, the lens becomes thick and its focal length decreases. d) Near point :-   The minimum distance at which the eye can  see objects  clearly is called the near point or least distance of distinct vision. For a normal eye it is 25cm. e) Far point :-   The farthest distance upto which the eye can see objects  clearly is called the far point of the eye. For a normal eye it is between 25cm and infinity.     
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THE HUMAN EYE                                                                                  1a) The human eye :-           The human eye is the sense organ which helps us to see the  colourful world around us.       The human eye is like a camera. Its lens system forms an image on a light sensitive screen called retina. The eye ball is almost spherical in shape with a diameter of about 2.3cm. Light enters the eye through a transparent membrane called cornea.  Behind the cornea is  a  muscular diaphragm called iris which has an opening called pupil. The pupil controls the amount of light entering the eye. The eye lens helps to focus the image of objects on the retina. The ciliary muscles helps to change the curvature of the lens and to change its focal length. b) Working of the eye :-      The eye lens forms a real inverted image of the object on the retina. The light sensitive cells in the retina then produce electrical signals which are carried by the optic nerves to the brain. The brain  processes the information and sends the message to the eye and then we  see the object. c) Power of accomodation of the eye :-     The ability of the eye lens to see both near and distant objects by adjusting  its focal length is called the power of accommodation of the eye.    The eye lens is composed of a fibrous jelly like material. Its curvature can be changed to some extent by the ciliary muscles. The change in the curvature of the eye lens can change its focal length. When the muscles are relaxed, the lens becomes thin and its focal length increases and when the muscles contract, the lens becomes thick and its focal length decreases. d) Near point :-   The minimum distance at which the eye can  see objects  clearly is called the near point or least distance of distinct vision. For a normal eye it is 25cm. e) Far point :-   The farthest distance upto which the eye can see objects  clearly is called the far point of the eye. For a normal eye it is between 25cm and infinity.     2) Defects of vision and their correction :- i) Myopia or near sightedness :-               Myopia is a defect of vision in which a person can see nearby objects clearly but cannot see distant objects clearly because the image is formed in front of the retina.    This may be due to:- i) Increase in curvature of the eye lens ii) Increase in the length of the eye ball    It can be corrected by using suitable concave lens. Myopic eye Correction using concave lens
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THE HUMAN EYE                                                                                  1a) The human eye :-           The human eye is the sense organ which helps us to see the  colourful world around us.       The human eye is like a camera. Its lens system forms an image on a light sensitive screen called retina. The eye ball is almost spherical in shape with a diameter of about 2.3cm. Light enters the eye through a transparent membrane called cornea.  Behind the cornea is  a  muscular diaphragm called iris which has an opening called pupil. The pupil controls the amount of light entering the eye. The eye lens helps to focus the image of objects on the retina. The ciliary muscles helps to change the curvature of the lens and to change its focal length. b) Working of the eye :-      The eye lens forms a real inverted image of the object on the retina. The light sensitive cells in the retina then produce electrical signals which are carried by the optic nerves to the brain. The brain  processes the information and sends the message to the eye and then we  see the object. c) Power of accomodation of the eye :-     The ability of the eye lens to see both near and distant objects by adjusting  its focal length is called the power of accommodation of the eye.    The eye lens is composed of a fibrous jelly like material. Its curvature can be changed to some extent by the ciliary muscles. The change in the curvature of the eye lens can change its focal length. When the muscles are relaxed, the lens becomes thin and its focal length increases and when the muscles contract, the lens becomes thick and its focal length decreases. d) Near point :-   The minimum distance at which the eye can  see objects  clearly is called the near point or least distance of distinct vision. For a normal eye it is 25cm. e) Far point :-   The farthest distance upto which the eye can see objects  clearly is called the far point of the eye. For a normal eye it is between 25cm and infinity.     2) Defects of vision and their correction :- i) Myopia or near sightedness :-               Myopia is a defect of vision in which a person can see nearby objects clearly but cannot see distant objects clearly because the image is formed in front of the retina.    This may be due to:- i) Increase in curvature of the eye lens ii) Increase in the length of the eye ball    It can be corrected by using suitable concave lens. Myopic eye Correction using concave lens ii) Hypermetropia or far sightedness :-     Hypermetropia is a defect of vision in which a person can see distant objects clearly but cannot see nearby objects clearly 
because the image is formed behind the retina.    This may be due to:- i)  Decrease in curvature of eye lens ii) Decrease in the length of the eye ball      It can be corrected by using a suitable convex lens. Hypermetropic eye Correction using convex lens