Question

A concave lens made of material of refractive index 1.6 is immersed in a medium of refractive index 2.0. The two surfaces of the concave lens have the same radius of curvature 0.2 m. The lens will behave as a

• A. Divergent lens of focal length 0.4 m
• B. Divergent lens of focal length 0.5 m
• C. Convergent lens of focal length 0.4 m
• D. Convergent lens of focal length 0.5 m

Answer 1

The correct option is D

Convergent lens of focal length 0.5 m

$\frac{1}{F}=(\frac{1.6}{2}-1)(\frac{1}{-0.2}-\frac{1}{0.2})$

$=\frac{0.4}{2}\times \frac{1}{0.1}$

F = 0.5

It will behave as a converging lens.