Q 12-09-179JEE MainJEE Main 2020 (6 Sep, Shift 2)Easy
A double convex lens has power $P$ and the same radius of curvature $r$ for both surfaces. The radius of curvature of a surface of a plano-convex lens made of the same material with power $1.5P$ is:
Answer: (D) $\dfrac r3$
Double convex: $P = (\mu - 1)\dfrac2r$.
Plano-convex with curved surface of radius $R$: $1.5P = (\mu - 1)\dfrac1R$.
$$\frac{1}{R} = 1.5\times\frac2r = \frac3r \Rightarrow R = \frac r3$$
Solution by Sreeraj P, M.Sc Physics