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

  $\mathrm{asin}\mathrm{\theta }=\frac{\mathrm{\lambda }}{2}$

• B

  $\mathrm{acos}\mathrm{\theta }=\frac{3\mathrm{\lambda }}{2}$

• C

  $\mathrm{asin}\mathrm{\theta }=\mathrm{\lambda }$

• D

  $\mathrm{asin}\mathrm{\theta }=\frac{3\mathrm{\lambda }}{2}$