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प्रश्न
My grandfather uses a bifocal lens in his spectacle. Explain why.
उत्तर
Grandfather suffers from both myopia and hypermetropia. In few old age people near and distance vision is affected. In bifocal lens upper part is concave lens to correct myopia and lower part is convex lens for near vision. Hence grandfather uses bifocal lens in his spectacle.
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संबंधित प्रश्न
The distance between principal focus and optical centre of the lens is _________.
- diameter
- focal length
- principal axis
- optical centre
Define focal length of a divergent lens.
Suppose you have focused on a screen the image of candle flame placed at the farthest end of the laboratory table using a convex lens. If your teacher suggests you to focus the parallel rays of the sun, reaching your laboratory table, on the same screen, what you are expected to do is to move the:
(a) lens slightly towards the screen
(b) lens slightly away from the screen
(c) lens slightly towards the sun
(d) lens and screen both towards the sun
An image formed by a concave ______ cannot be obtained on a screen.
A concave lens always forms a virtual image.
Explain why, a stick half immersed in water appears to be bent at the surface. Draw a labelled diagram to illustrate your answer.
Write the new Cartesian sign convention for spherical lenses.
Two lenses A and B have power of (i) +2D and (ii) −4D respectively. What is the nature and focal length of each lens?
If a spherical lens has a power of, −0.25 D, the focal length of this lens will be :
(a) −4 cm
(b) −400 mm
(c) −4 m
(d) −40 cm
If a spherical lens has a power of, −0.25 D, the focal length of this lens will be :
(a) −4 cm
(b) −400 mm
(c) −4 m
(d) −40 cm
What are the three principal rays that are drawn to construct the ray diagram for the image formed by a lens? Draw diagrams to support your answer.
A convex lens forms an image of an object equal to the size of the object. Where is the object placed in front of the lens?
A lens forms the image of an object placed at a distance 15 cm from it, at a distance 60 cm in front of it. Find the nature of image.
Complete the ray diagram to show how the rays pass into and out of the lens?
Which diagram shows image formation of an object on a screen by a converging lens?
Complete the following table for convex lens:
| Sr. No. | Position of the object | Position of the image | Nature of the image |
| 1. | Beyond 2F1 | __________________ | ________________________ |
| 2. | __________________ | At infinity | ________________________ |
| 3. | __________________ | __________________ | Real, inverted and enlarged |
