Q. A biconvex lens has a radius of curvature of magnitude $20cm$. Which one of the following options describe best the image formed of an object of height $2\ cm$ placed $30\ cm$ from the lens
A) Real, inverted, height $= 1\ cm$
B) Virtual, upright, height $= 1\ cm$
C) Virtual, upright, height $= 0.5\ cm$
D) Real, inverted, height $= 4\ cm$
Explanation
(d) $\frac{1}{f} = (\mu - 1)\left( \frac{1}{R_{1}} - \frac{1}{R_{2}} \right)$
If $R_{1} = R,\ R_{2} = - R$
$f = \frac{R}{2(\mu - 1)} = \frac{20}{2(1.5 - 1)} = 20\ cm$
$\because\frac{I}{O} = \frac{f}{f + u}$
$\frac{I}{2} = \frac{20}{20 - 30} = - 2$
$\Rightarrow I = - 4\ cm$
Image is Real and inverted
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.