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.......
Light is emitted due to the de-excitaton of electrons from higher orbits of the various atoms of the light source.The de-excitation can also be to different levels in different atoms resulting in emission of different wavelengths.A light source will have numerous atoms in it.When you take two light sources it is not possible for all the atoms to get de-excited to the same shell at the same time(causing phase difference) that is why two independent sources cannot be coherent.