Question

A hollow concave lens is made of very thin transparent material. It can be filled with air or either of two liquids $L_{1}or{L}_2$ having refractive indices $n_{1}or{n}_2$, respectively $(n_2>n_1>1)$. The lens will diverge a parallel beam of light if it is filled with

• A. $\text{air and placed in air}$
• B. $\text{air and immersed in}$ $L_1$
• C. $L_1$ and immersed in $L_2$
• D. $L_2$ and immersed in $L_1$

Answer 1

Answer: (D)

$L_2$ and immersed in $L_1$

filled with $L_2$ and immersed in $L_1$

$f=\frac{n_2-n_1}{-R}+\frac{n_1-n_2}{R}=-\frac{2(n_2-n_1)}{R}$

the concave lens would acts as diverging lens as focal length is negative and the parallel rays would get diverge
option $D$ is correct