Q 12-09-222NEETNEET 2022Top questionEasy
A biconvex lens has radii of curvature, $20$ cm each. If the refractive index of the material of the lens is $1.5$, the power of the lens is
Answer: (D) $+5$ D
Lens maker's formula with $R_1 = +20$ cm, $R_2 = -20$ cm:
$$\frac{1}{f} = (\mu - 1)\left(\frac{1}{R_1} - \frac{1}{R_2}\right) = 0.5 \times \frac{2}{20} = \frac{1}{20}\ \text{cm}^{-1}$$
$f = 20$ cm $= 0.2$ m, so $P = \dfrac{1}{0.2} = +5$ D.
Solution by Sreeraj P, M.Sc Physics