Question

# Two identical thin plano-convex glass lenses (refractive index ) each having radius of curvature of are placed with their convex surfaces in contact at the centre. The intervening space is filled with oil of refractive index . The focal length of the combination is

A
B
C
D
Hard
Updated on : 2022-09-05
Solution
Verified by Toppr
Correct option is D)

## Here the light passes through three refracting media, as shown in the figure.Media has a refractive index and radius of curvature . While medium has a refractive index of and it acts as a concave lens.Let the focal length of the three media be .Applying the lens makers formulaFor media , since it is a plano convex lens.For media ,For media ,Since media are similar we can writeFor applying the formula for equivalents lenses,Hence the correct answer is option (D).

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