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

Answer 1

Answer: (D)

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