Question

Two thin symmetrical lenses of different nature and of different material have equal radii of curvature $R=15cm$. The lenses are put close together and immersed in water $({\mu }_w=4/3)$. The focal length of the system in water is $30cm$. The difference between refractive indices of the two lenses is

• A. $1/2$
• B. $1/4$
• C. $1/3$
• D. $3/4$

Answer 1

The correct option is C $1/3$

focal length be $f=30$

$\frac{4/3-{\mu }_1}{R}+\frac{{\mu }_2-4/3}{R}=\frac{1}{f}$

$\frac{\Delta \mu }{15}=\frac{1}{30}$

$\Delta \mu =\frac{1}{2}$

option $A$ is correct