Question

Determine the focal length of bi-convex lens of radii of curvatures $12cm$ and $18cm$ . What will be its focal length if the lens is immersed in water? $(\mu =3/2,{\mu }_w=4/3)$

Answer 1

$\frac{1}{f}=\left(\frac{\mu {}_g^a}{\mu {}_w^a}-1\right)\left(\frac{1}{R_1}-\frac{1}{R_2}\right)$

By substituting the values given in the above equation we get

$\frac{1}{f}=\left(\frac{1.5}{\frac{4}{3}}-1\right)\left(\frac{1}{12}+\frac{1}{18}\right)$

$=57.6cm$