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CGP EDU Academic Team
Published on: September 12, 2026
The focal length of a plano convex lens is f and its refractive index is 1.5 . It is kept over a plane glass plate with its curved surface touching the glass plate. The gap between the lens and the glass plate is filled by a liquid. As a result, the effective focal length of the combination becomes 
. Then the refractive index of the liquid is
Text Solution
Verified by ExpertsThe correct answer is:
C
According to lens maker's formula
The focal length of plane convex lens is
or 
The focal length of liquid lens is
[Using (i)]
Effective focal length of the combination is
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