Question

An air bubbles is inside water. The refractive index of water is 4/3. At what distance from the air bubble should a point be placed to form a real image at the same distance from the bubble -

• A. 2R
• B. 3R
• C. 4R
• D. The air bubble cannot form a real image of real object

Answer 1

Answer: (D)

The air bubble cannot form a real image of real object

$\begin{array}{c}\text{weknow that}\\ \begin{array}{cc}\frac{1}{f}& =(\frac{{\mu }_l}{{\mu }_m}-1)(\frac{1}{R_1}-\frac{1}{R_2})\\ \text{Here}{\mu }_{\text{lens}}& =1{\mu }_m=4/3R_1=R{R}_2=-R\\ \frac{1}{f}& =(\frac{3}{4}-1)(\frac{1}{R}+\frac{1}{R})\end{array}\end{array}$

$\begin{array}{c}\frac{1}{f}\text{isnegative so it acts as concave lens}\\ \text{A concave lens cannot form real image.}\end{array}$