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Question

A man is trying to start a fire by focusing sunlight on a piece of paper using an equiconvex lens of focal length 10 cm. The diameter of the sun is 1.39×109m and its mean distance from the earth is 1.5×1011 m, the diameter of the sun's image on the paper is

A
3.1×104m
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B
6.5×105m
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C
6.5×104m
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D
9.2×104m
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Solution

The correct option is D 9.2×10−4mMagnification of convex lens, m=−ff−uHere, f=10cm=10×10−2m,u=1.5×1011m∴m=−10×10−210×10−2−1.5×1011=6.67×10−13∴ Diameter of the image,d=m×1.39×109=6.67×10−13×1.39×109=9.27×10−4m Hence, the correct option is (D)

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