two independent light sources cannot act as coherent sources.why?
if 2 sources r independent i.e. not coherent, phase difference between d waves emmited by them changes very rapidly.
At one instant d waves will be in phase & at d another instant it will be out of phase. Intensity at that pt. changes very rapidly between minima & maxima. Thus every pt. on screen will appear equally bright and no interference bands will be observed..... SO 2 INDEPENDENT LIGHT SOURCES CANNOT ACT AS COHERENT SOURCES.
Hope that clears ur point.......