Question

A biconvex lens of focal length $f$ and radii of curvature of both the surfaces $R$ is made of a material of refractive index $n_1$. This lens is placed in a liquid of refractive index $n_2$. Now this lens will behave like

• A. either as a convex or as a concave len depending solely on R
• B. a convex lens depending on $n_1$ and $n_2$
• C. a concave lens depending on $n_1$ and $n_2$
• D. a convex lens of same focal length irrespective of R, $n_1$ and $n_2$

Answer 1

Answer: (B), (C)

The convex lens will be converging, i.e., will behave like a convex lens when $n_1>n_2$.
The same convex lens will be diverging, i.e., will behave like a concave lens when $n_1<n_2$
So, the convex lens will behave like a convex or a concave lens depending on the values of $n_1$ and $n_2$.