Points of similarity:
|
Camera |
Human eye |
|
2. A real and inverted image is formed on the photographic film. 3. Diaphragm controls the amount of light entering the camera. 4. Time of exposure is controlled by a shutter. |
1. Image is formed by the eyelens (a convex lens) made of fibrous, jelly like material. 2. A real and inverted image is formed on the retina. 3. Pupil in the iris controls the amount of light entering the eye. 4. Time of exposure is controlled by the eyelids. |
Points of dissimilarity:
|
Camera |
Human eye |
|
1. Focal length of camera lens is fixed. 2. Focussing is done by changing the distance between the camera lens and the photographic film. 3. Photographic film retains the image permanently. 4. A photograph has to be changed for getting next image. 5. The angular region covered is about 60°. |
1. Focal length of eyelens can be changed with the help of ciliary muscles. 2. Focussing is done by changing the shape of the eyelens by the action of ciliary muscles. 3.The retina of the eye retains the impression of an image for about (1/16)th of a second. 4. The same retina can be used for viewing an unlimited number of images. 5. The angular region covered is about 150°. |
Define the following terms and give their values for a normal eye:
(i) Range of normal vision.
(ii) Least distance of distinct vision.
(iii) Near point of the eye.
(iv) Far point of the eye.
(v) Power of accommodation.
(a) What is myopia? State two reasons due to which this effect is caused.
(b) Draw a diagram to show the formation of image of a distant object by a myopic eye. How can such an eye defect be remedied?
Or
State two main causes of a person developing near sightedness. With the help of a ray diagram, suggest how he can be helped to overcome this disability.
