The distance between object and its two times magnified real image as produced by a convex lens is 45 cm. The focal length of the lens used is cm.
10
Real image, |m|=2 ⇒ v=2|u|; object and image on opposite sides
|u|+v=45 |u|=15 cm, v=30 cm
1f= 1v- 1u= 130+ 115= 330
f=10 cm
Answer: 10
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