Q. A zone plate of focal length $60cm$, behaves as a convex lens, If wavelength of incident light is $6000\ \mathring{\mathrm{A}}$, then radius of first half period zone will be
A) $36 \times 10^{- 8}m$
B) $6 \times 10^{- 8}m$
C) $\sqrt{6} \times 10^{- 8}m$
D) $6 \times 10^{- 4}m$
Explanation
(d) By using $f_{p} = \frac{r^{2}}{(2p - 1)\lambda}$
For first $HPZ\ r = \sqrt{f_{p}\lambda} = \sqrt{0.6 \times 6000 \times 10^{- 10}}$
$= 6 \times 10^{- 4}m$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.