A double convex lens of glass has both faces of the same radius of curvature 17 cm. Find its focal length if it is immersed in water. The refractive…

$\displaystyle \frac{1}{f}=\left(\frac{n_{g}}{n_{w}}-1\right)\left(\frac{1}{R_{1}}-\frac{1}{R_{2}}\right)$ For double convex lens $\displaystyle R_{1}=R$ and $\displaystyle R_{2}=-R$: $\displaystyle \frac{1}{f}=\left(\frac{1.5}{1.33}-1\right)\left(\frac{2}{R}\right)$ $\displaystyle =\left(\frac{1.5-1.33}{1.33}\right)\left(\frac{2}{17}\right)$ $\displaystyle f=66.5 \mathrm{~cm}$