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An effective power of a combination of 5 identical convex lenses which are kept in contact along the principal axis is 25D. Focal length of each of the convex lens is:
(2) 20 cm
Lenses in contact: Peq=P1+P2+ =5P
5P=25 D P=5 D
f= 1P= 15 m=20 cm
Answer: (2)
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