a) Discuss the Fraunhofer diffraction at a single slit. Obtain the condition for principal maximum and minimum. (10M) b) A plan wave of wavelength 5893 x 108 cm is incident normally on slit of width (4M) 0.5 mm and forms a diffraction pattern on a screen placed 1 m away from the slit. Calculate the separation of first dark band on either side of the central maximum.