The radius of curvature of each surface of a convex lens having...

The power of a lens is given by

${P}_{1} = \dfrac{1}{f}$

Using Lens Maker's formula,

${P}_{1} = ( 1 .8 - 1 ) \left(\dfrac{1}{{R}_{1}} - \dfrac{1}{{R}_{2}}\right) and </p><p>${P}_{2} = \dfrac{1}{{f}_{\text{immersed}}} = \left(\dfrac{1 .8}{1 .5} - 1\right)\left(\dfrac{1}{{R}_{1}} - \dfrac{1}{{R}_{2}}\right)$</p><p>Hence, the ratio is,</p><p>$\dfrac{{P}_{1}}{{P}_{2}} = \dfrac{( 1 .8 - 1 )}{\left(\dfrac{1 .8}{1 .5} - 1\right)} = \dfrac{0 .8 \times 1 .5}{0 .3} = 4$