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Two similar planoconvex lenses are combi...

Two similar planoconvex lenses are combined together in three different ways as shown in the adjoining figure. The ratio of the focal lengths in three cases will be

A

`2 : 2 : 1`

B

`1 : 1 : 1`

C

`1 : 2 : 2`

D

`2 : 1 : 1`

Text Solution

Verified by Experts

The correct Answer is:
B
(b) In each case, there is a combination of two plano-convex lenses placed close to each other. Focal length of combination `1/F=1/f+1/f` is same in all cases, so ratio of focal length in three cases is 1 : 1 : 1
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DC PANDEY ENGLISH-RAY OPTICS-Checkpoint 9.4
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