State the condition under which the phenomenon of diffraction of light takes place. Derive an expression for the width of the central maximum because of diffraction of light at a single slit. A slit of width 'a' is illuminated by a monochromatic light of wavelength 700 nm at normal incidence.
Calculate the value of 'a' for position of
1. First minimum at an angle of diffraction of 30°.
2. First maximum at an angle of diffraction of 30°. 5