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. $



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