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Question

# A convex lens of focal length 10 cm in contact with a concave lens of focal length 20 cm. This combination is used to focus an object positioned 30 cm infront of combination. The image will be formed at a distance of

A
30 cm
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B
40 cm
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C
50 cm
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D
60 cm
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Solution

## The correct option is D 60 cmGiven, f1=10 cm f2=−20 cm We know, 1F=1f1+1f2=110−120=2−120=120 Equivalent focal length F=20 cm Given, u=−30 cm Using lens formula, 1F=1v−1u ⇒120=1v+130 ⇒120−130=1v ⇒3−260=1v ⇒v=60 cm

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