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Question

# A convex lens of power 4 D is placed at a distance of 40 cm from a wall. At what distance from the lens should a candle be placed so that its image is formed on the wall?

A
1003 cm
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B
2003 cm
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C
5003 cm
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D
7003 cm
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Solution

## The correct option is B 2003 cmHere, f=1P=14D=14 m=25 cm Image has to be formed at the wall, hence image distance is, v=+40 cm. From Lens formula , 1v−1u=1f ⇒1u=1v−1f ⇒1u=140 cm−125 cm=−3200 cm Or, u=−2003 cm So, the candle should be placed at a distance 2003 cm from the lens on the opposite side of wall.

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