Question

A slit of width a is illuminated by red light of wavelength $ 6500\, \overset{\text{o}}{\mathop{\text{A}}}\, $ . If the first minimum falls at $ \theta =30{}^\circ , $ the value of $ a $ is

• A. $ 6.5\times {{10}^{-4}}mm $
• B. $ 1.3\,\,micron $
• C. $ 3250\,\overset{\text{o}}{\mathop{\text{A}}}\, $
• D. $ 2.6\times {{10}^{-4}}cm $

Answer 1

The Correct Option is B

According to principle of diffraction
$ a\sin \theta =n\lambda $ where $
n= $ order of secondary minimum $ \therefore $
$ a\sin 30{}^\circ =1\times (6500\times {{10}^{-10}}) $
or $ a=1.3\times {{10}^{-6}}m $ or $ a=1.3\text{ }micron $