In a Young's double slit experiment, (i) deduce the conditions for constructive and destructive interference. Hence, write the expression for the distance between two consecutive bright or dark fringe.
(ii) what change in the interference pattern do you observe, if the two slits, `S_1 and S_2` are taken as point sources?
(iii) plot a graph of the intensity distribution versus path difference in this experiment. Compare this with the intensity distribution of fringes due to diffraction at a single slit. What important difference do you observe?