question_answer

A thin converging lens has a focal length\['f'\] in air. If it is completely immersed in a liquid, briefly explain how the focal length of the lens will vary?                                 

Answer:

                According to lens maker's formula, \[\frac{1}{f}=(\mu -1)\left( \frac{1}{{{R}_{1}}}-\frac{1}{{{R}_{2}}} \right)\]                 i.e.,        \[f\propto \frac{1}{\mu -1}\] As \[^{l}{{\mu }_{g}}{{<}^{a}}{{\mu }_{g}}\] so the focal length of the lens will increase when it is completely immersed in the liquid.