Optics Question 207
Question: A zone plate of focal length $ 60cm, $ behaves as a convex lens, If wavelength of incident light is $ 6000{AA}, $ then radius of first half period zone will be
[RPMT 2001]
Options:
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. $
Show Answer
Answer:
Correct Answer: D
Solution:
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. $
