Question

A converging lens has focal length of 20 cm in air. It is made of a material of refractive index 1.6. It is immersed in a liquid of refractive index 1.3, what will be its new focal length ?

Answer 1

we know, convex lens is also known as converging lens.

a/c to question,

focal length of converging lens , f = 20cm

refractive index of lens , $\mu$ = 1.6

refractive index of liquid in which lens is immersed, $\mu_l$ = 1.3

use formula, $f_l=\frac{\mu-1}{\frac{\mu}{\mu_l}-1}\times f$

= $\frac{1.6-1}{\frac{1.6}{1.3}-1}\times20$

= $\frac{0.6}{0.23}\times20$

= $\frac{12}{0.23}$

= 52

hence, new focal length of lens is 52cm