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प्रश्न
The lens mentioned in 6(b) above is of focal length 25cm. Calculate the power of the lens.
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उत्तर
Focal length of a convex lens is always positive.
Given: f = +25 cm
`therefore P=1/f`
`P=1/25`
`P=+0.04D`
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संबंधित प्रश्न
Calculate the focal length of a corrective lens having power +2D.
Give the usual name for the following:
A point inside a lens through which the light passes undeviated.
What is the power of a convex lens of focal length 0.5 m?
Two lenses A and B have focal lengths of +20 cm and, −10 cm, respectively.
(a) What is the nature of lens A and lens B?
(b) What is the power of lens A and lens B?
(c) What is the power of combination if lenses A and B are held close together?
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 double convex lens has focal length 25 cm. The radius of curvature of one of the surfaces is double of the other. Find the radii, if the refractive index of the material of the lens is 1.5.
Consider the situation described in the previous problem. Where should a point source be placed on the principal axis so that the two images form at the same place?
A diverging lens of focal length 20 cm and a converging lens of focal length 30 cm are placed 15 cm apart with their principal axes coinciding. Where should an object be placed on the principal axis so that its image is formed at infinity?
How is accommodation produced?
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.
