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प्रश्न
What do you understand by the power of a lens? Name one factor on which the power of a lens depends.
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उत्तर
The power of a lens is a measure of the degree of convergence or divergence of light rays falling on it. It is defined as the reciprocal of the focal length of a lens in metres.
i.e., Power = `1/"focal length of lens (in metre)"`
Therefore, the power of a lens depends on the focal length.
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संबंधित प्रश्न
State power of a lens S.I. unit.
Define 1 dioptre of power of a lens.
Find the focal length of a lens of power −2.0 D. What type of lens is this?
A doctor has prescribed a corrective lens of power +1.5 D. Find the focal length of the lens. Is the prescribed lens diverging or converging?
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.
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(b) What is the magnification in this case?
(c) Is the magnification equal to the magnifying power in this case? Explain.
What is the nature of a lens whose power is, −4 D?
An object of height 4 cm is placed at a distance of 15 cm in front of a concave lens of power, −10 dioptres. Find the size of the image.
The power of a lens is +2.0D. Its focal length should be :
Define the term focal length of a lens.
How is the power of a lens related to its focal length?
How does the power of a lens change if its focal length is doubled?
Express the power (with sign) of a concave lens of focal length 20 cm.
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.
A 5.0 diopter lens forms a virtual image which is 4 times the object placed perpendicularly on the principal axis of the lens. Find the distance of the object from the lens.
Find the power of a convex lens of focal length of + 25 cm.
Increase in the converging power of eye lens cause ‘hypermetropia'
Match the following:
| Column - I | Column - II | ||
| 1 | Retina | a | Path way of light |
| 2 | Pupil | b | Far point comes closer |
| 3 | Ciliary muscles | c | near point moves away |
| 4 | Myopia | d | Screen of the eye |
| 5 | Hypermetropia | e | Power of accommodation |
A convex lens with radii of curvature R1 = R2 is immersed in water. Assuming that the refractive indices of glass and water are 3/2 and 4/3 respectively, its focal length f1 in comparison to that in air, f, is ______.
A point object is placed at O in front of a glass sphere as shown in figure.
Show the formation of the image by the sphere.
