Question

A planoconcave lens is placed on a paper on which a flower is drawn. How far above its actual position does the flower appear to be?

• A. 10 cm
• B. 15 cm
• C. 50 cm
• D. None of these

Answer 1

Answer: (A)

Considering refraction at the curved surface,
$u =-20, \mu_2=1 $
$\mu_1=3 / 2, R =+20$
Applying $\frac{\mu_2}{ v }-\frac{\mu_1}{ u }=\frac{\mu_2-\mu_1}{ R }$
$\Rightarrow \frac{1}{v}-\frac{3 / 2}{-20}=\frac{1-3 / 2}{20} $
$\Rightarrow v=-10$
i.e., $10 \,cm$ below the curved surface or $10\, cm$ above the actual position of flower.