## Question

A convex lens of glass (refractive index 1.5) has both surfaces of radius of curvature 20 cm. Find its focal length and nature when it immersed in a liquid of refractive index 1.75.

### Solution

–70 cm

Refractive index of glass with respect to liquid = refractive index of air with respect to liquid × refractive index of glass with respect to air. That is

The focal length of the lens immersed in the liquid is given by

Here *R*_{1} = +20 cm and *R*_{2} = – 20 cm.

Since the sign of *f* is negative, the nature of the **lens is concave.**

#### SIMILAR QUESTIONS

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