Question

Two identical glass equiconvex lenses of focal length are kept in contact. The space between the two lenses is filled with water . The focal length of the combination is

A

B

C

D

Medium
Solution
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Correct option is D)

Water in between the lens can be considered to be a concave lens of refractive index of water as shown in the figure. This suggests that the radius of curvature of all the lenses is same.
Consider the convex lens-

hence

For the concave lens,


Power of the lenses get added,


Hence  

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