Question

Direction of the first secondary maximum in the Fraunhofer diffraction pattern at a single slit is given by (a is the width of the slit)

• A. $\mathrm{asin}\theta =\frac{\lambda }{2}$
• B. $a\cos \theta =\frac{3\lambda }{2}$
• C. $\mathrm{asin}\theta =\lambda$
• D. $a\sin \theta =\frac{3\lambda }{2}$

Answer 1

The correct option is D $a\sin \theta =\frac{3\lambda }{2}$

For $n^{th}$ secondary maxima path difference
$d\sin \theta =(2n+1)\frac{\lambda }{2}\Rightarrow <br/>a\sin \theta =\frac{3\lambda }{2}<br/>$