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प्रश्न
How is accommodation produced?
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उत्तर
Accommodation is achieved with the help of ciliary muscles.
To focus the distant objects, the ciliary muscles are relaxed causing the eye lens to become thin and thus increasing the focal length of the eye lens.
To form the image of a near object on the retina, the ciliary muscles contract and thereby pull the ends of the choroid closer. Thus, the eye lens thickens to shorten its focal length and converges the rays to form the image.
In this manner, by changing the focal length of the eye lens, the image of the objects at different distances is brought to focus on the retina.
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संबंधित प्रश्न
What does sign of power (+ve or –ve) indicate?
What is the focal length of a convex lens of focal length 30 cm in contact with a concave lens of focal length 20 cm? Is the system a converging or a diverging lens? Ignore thickness of the lenses.
The optician's prescription for a spectacle lens is marked +0.5 D. What is the:
(a) nature of spectacle lens?
(b) focal length of spectacle lens?
State the condition for the following a ray passes undeviated through the lens .
Mohan obtained a sharp inverted image of a distant tree on the screen placed behind the lens. He then moved the screen and tried to look through the lens in the direction of the object. He would see:
(1) a blurred image on the wall of the laboratory.
(2) an erect image of the tree on the lens.
(3) no image as the screen has been removed
(4) an inverted image of the tree at the focus of the lens.
Surabhi from std. X uses spectacle. The power of the lenses in her spectacle is 0.5 D.
Answer the following questions from the given information:
- Identify the type of lenses used in her spectacle.
- Identify the defect of vision Surabhi is suffering from.
- Find the focal length of the lenses used in her spectacle.
The power of a lens is +2.0 D. Find its focal length and state the kind of lens.
A convex lens is of focal length 20 cm. Find its power.
An object is placed in front of a converging lens. Obtain the conditions under which the magnification produced by the lens is
- negative and
- positive.
The same size images are formed by a convex lens when the object is placed at 20 cm or at 10 cm from the lens. The focal length of convex lens is ______ cm.
