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How unit of power related to focal length of a lens?
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Define 1 dioptre of power of a lens.
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A convex lens forms a real and inverted image of a needle at a distance of 50 cm from it. Where is the needle placed in front of the convex lens if the image is equal to the size of the object? Also, find the power of the lens.
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Find the power of a concave lens of focal length 2m.
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Find the focal length of a lens of power −2.0 D. What type of lens is this?
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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?
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You have two lenses A and B of focal lengths +10 cm and –10 cm, respectively. State the nature and power of each lens. Which of the two lenses will form a virtual and magnified image of an object placed 8 cm from the lens? Draw a ray diagram to justify your answer
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A student uses a lens of focal length 40 cm and another of –20 cm. Write the nature and power of each lens
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What can you see in a completely dark room? If you switch on an electric bulb in this dark room as a light source, explain how you could now see:
(a) the electric bulb
(b) a piece of white paper
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Consider two statements A and B given below:
A: real image is always inverted
B: virtual image is always erect
Out of these two statements:
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Which one of the following materials cannot be used to make a lens?
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The lens A has a focal length of 25 cm whereas another lens B has a focal length of 60 cm. Giving reason state, which lens has more power: A or B.
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Name the physical quantity whose unit is dioptre.
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Which type of lens has (a) a positive power, and (b) a negative power?
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Which of the two has a greater power: a lens of short focal length or a lens of large focal length?
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How is the power of a lens related to its focal length?
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Which has more power : a thick convex lens or a thin convex lens, made of the same glass? Give reason for your choice.
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The focal length of a convex lens is 25 cm. What is its power?
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What is the power of a convex lens of focal length 0.5 m?
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A converging lens has focal length of 50 mm. What is the power of the lens?
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