Question

A double convex lens made of a material of refractive index 1.5 and having a focal length of 10 cm is immersed in liquid of refractive index 3.0. The lens will behave as

• A. Diverging lens of focal length 10 cm
• B. Diverging lens of focal length $\frac{10}{3}cm$
• C. Converging lens of focal length $\frac{10}{3}cm$
• D. Converging lens of focal length 30 cm

Answer 1

The correct option is A Diverging lens of focal length 10 cm

By using $\frac{f_i}{f_a}=\frac{{}_a{\mu }_g-1}{{}_l{\mu }_g-1}\Rightarrow \frac{f_l}{+10}=\frac{1.5-1}{\frac{1.5}{3}-1}\Rightarrow f_l=-10cm$ (i.e. diverging lens)