Optics Question 194
Question: A slit of width $ a $ is illuminated by white light. For red light $ (\lambda =6500{AA}) $ , the first minima is obtained at $ \theta =30^{o}. $ Then the value of a will be
[MP PMT 1987; CPMT 2002]
Options:
A) $ 3250{AA} $
B) $ 6.5\times {{10}^{-4}}mm $
C) 1.24 microns
D) $ 2.6\times {{10}^{-4}}cm $
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Answer:
Correct Answer: C
Solution:
For first minima $ \theta =\frac{\lambda }{a} $ or $ a=\frac{\lambda }{\theta } $
$ \therefore a=\frac{6500\times {{10}^{-8}}\times 6}{\pi } $ (As 30o = $ \frac{\pi }{6} $ radian) $ =1.24\times {{10}^{-4}}cm=1.24 $ microns
