    Question

# A 10 cm tall candle when viewed using a convex lens appears to be 20 cm tall as shown in the below figure. The focal length of the lens is 5 cm. What is the object distance? A

10 cm

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B

5 cm

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C

20 cm

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D

2.5 cm

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Solution

## The correct option is D 2.5 cm Given: Object height =h=10 cm Image height =h′=20 cm Focal length of the convex lens f=5 cm From magnification formula: m=h′h=2010=2 also m=vu=2, where u is the object distance and v is the image distance. ⇒v=2u From lens formula, 1v−1u=1f. or, 12u−1u=15 ⇒u=−2.5 cm Therefore, 2.5 cm is the object distance from lens.  Suggest Corrections  0      Similar questions  Related Videos   Lens Formula, Magnification and Power of Lens
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