Question

A lens has a power of + 5 D in air. what will be it's power if it is completely immersed in water?(given- refractive index of gas = 3/2 ; refractive index of water = 4/3)
(a) 5/3 (b) 3/2 (c) 1/2 (d) 8/9

Answer 1

$$\begin{gathered} Powerafteremerginginwater,\frac{P\text{'}}{P}=\frac{({\mu }_1-{\mu }_2)}{{\mu }_2({\mu }_1-1)} \\ \Rightarrow P\text{'}=\frac{3/2-4/3}{4/3(3/2-1)}=5/4D \end{gathered}$$