Q.
In a Fraunhofer diffraction at single slit of width d with incident light of wavelength 5500A˚, the j first minimum is observed, at angle 30∘. The first secondary maximum is observed at an angle θ=
Slit width =d λ=5500A˚=5.5×10−7m,θn​=30∘
For first secondary minima, dsinθn​=λ d=sinθn​λ​=sin30∘5.5×10−7​ =11×10−7m
For first secondary maxima, dsinθn​=23λ​
i.e., sinθn​=2d3λ​ =2×11×10−73×5.5×10−7​ sinθn​=43​ or θn​=sin−1(3/4)