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प्रश्न
If an object is placed 21 cm from a converging lens, the image formed is slightly smaller than the object. If the object is placed 19 cm from the lens, the image formed is slightly larger than object. The approximate focal length of the lens is ______.
विकल्प
20 cm
18 cm
10 cm
5 cm
उत्तर
If an object is placed 21 cm from a converging lens, the image formed is slightly smaller than the object. If the object is placed 19 cm from the lens, the image formed is slightly larger than object. The approximate focal length of the lens is 10 cm.
Explanation:
We know that a converging lens forms an image of same size as object when object is placed at a distance of 2f from the lens. It is given that the image is smaller than the object if object is kept at a distance of 21 cm. Similarly, the image is bigger than the object if object is kept at a distance of 19 cm. Therefore, at 20 cm, the distance should be 2f. This means that the focal length is approximately 10 cm.
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संबंधित प्रश्न
A converging lens is used to produce an image of an object on a screen,object on a screen. What change is needed for the image to be formed nearer to the lens?
(a) increase the focal length of the lens
(b) insert a diverging lens between the lens and the screen
(c) increase the distance of the object from the lens
(d) move the object closer to the lens
Fill in the following blank with suitable word:
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a converging lens, and which is
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(c) prismatic lenses
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