Question

An equi convex lens is made of a material of refractive index ${\mu }_1$ and is placed inside two liquids of refractive indices ${\mu }_2$ and ${\mu }_3$ as shown with ${\mu }_2>{\mu }_1>{\mu }_3$. A wide, parallel beam of light is incident on the lens from the left. The lens will give rise to:

• A. A single convergent beam
• B. Two different convergent beams
• C. Two different divergent beams
• D. A convergent and divergent beam

Answer 1

The correct option is D

A convergent and divergent beam

Using $\frac{1}{f}=({\mu }_r-1)(\frac{1}{R_1}-\frac{1}{R_2})$
$f>0$ for lower half of lens as ${\mu }_r=\frac{{\mu }_1}{{\mu }_2}>1$
$f<0$ for upper half of lens as ${\mu }_r=\frac{{\mu }_1}{{\mu }_2}<1$
So, lower half acts as convergent lens and upper half as divergent lens.