Question

A bi-convex lens of glass $(n_g=\frac{3}{2})$ is immersed in water $(n_w=\frac{4}{3}).$ The ratio of new focal length of the lens to the focal length of lens in air is n. The value of n is:___

Answer 1

$\frac{1}{f_1}=(\frac{3}{2}-1)(\frac{1}{R_1}-\frac{1}{R_2})[Using:Lensmake{r}^{\prime }sformula]\frac{1}{f_2}=(\frac{\frac{3}{2}}{\frac{4}{3}}-1)(\frac{1}{R_1}-\frac{1}{R_2})\frac{f_2}{f_1}=\frac{\left(\frac{1}{2}\right)}{\left(\frac{1}{8}\right)}\frac{f_2}{f_1}=4$