Question

A convex lens made up of glass of refractive index $1.5$ is dipped into a medium
(i) refractive index $1.65$ and
(ii) refractive index $1.33$
find nature and focal length of lens in both case.

Answer 1

The focal length of lens in liquid

$f_l=\frac{n_g-1}{\frac{n_g}{n_l}-1}{f}_a$

1).

$\frac{n_g}{n_l}=\frac{1.5}{1.65}$

We get the value is less than unity.

Hence, convex in liquid behaves as diverging lens as the focal lengths are of opposite sign.

2).

$\frac{n_g}{n_l}=\frac{1.5}{1.33}>1$

Hence the lens will acts as a converging lens