﻿ The focal length of a convex lens in air is 20 cm. What will be its focal length if it is immersed in a liquid of refractive index 1.35? Refractive index of glass is 1.50.   : Kaysons Education

# The Focal Length Of A Convex Lens In Air Is 20 Cm. What Will Be Its Focal Length If It Is Immersed In A Liquid Of Refractive Index 1.35? Refractive Index Of Glass Is 1.50.

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## Question

### Solution

Correct option is

90.8 cm

The focal length f of a lens in air is given by

Where n is refractive index of the material (glass) of the lens with respect to air. Here f = 20 cm, n = ang = 1.50.

Let the focal length of the lens immersed in the liquid be f. Now, in the above formula, n will be refractive index of glass with respect to liquid. That is

n = lng

Dividing eq. (i) by (ii), we get

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