Question

A thin glass lens (refractive index = 1.5) has an optical power of 5D in air. Its optical power in a liquid of refractive index 1.6 is

• A. $1D$
• B. $-1D$
• C. $-\frac{5}{8}D$
• D. $\frac{5}{8}D$

Answer 1

The correct option is C $-\frac{5}{8}D$

$\frac{P_a}{P_m}=\frac{({\mu }_g-1)}{(\frac{{\mu }_g}{{\mu }_1}-1)}\Rightarrow \frac{-5}{P_m}=\frac{0.5}{\frac{1.5-1.6}{1.6}}.HencePm=-\frac{5}{8}D$