Question

A plano-convex lens fits exactly into a plano-concave lens. Their plane surfaces are parallel to each other. If the lenses are made of different material of refractive indices and and R is the radius of curvature of the curved surface of the lenses, then focal length of the combination is :

A

B

C

D

Hard
Updated on : 2022-09-05
Solution
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Correct option is A)


Lens maker formula:                .......(1)

For Plano-convex lens:              

Using (1),                        

For Plano-concave lens:              

Using (2),                        

Thus focal length of combination,
 

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