# which waves give rise to interference pattern in a double slit diffraction experiment

In a double slit experiment,the fringes obtained on screen are due to superposition of single slit diffraction from each slit and the double slit interference pattern,

when we talk about single slit diffraction,we say the single slit is divided into many number of slits and the waves originating from them superimpose to produce the diffraction pattern on the screen,this means all the rays originating from each of the slits are engaged within themselves,

what waves are free from the slits which superimpose to give rise to the double slit interference pattern.

• All of them. Note that the Huygen construct is just one way to get intuition into the problem, and generally not the best for more complex situations. – Jon Custer Mar 21 '19 at 16:51
• @Jon Custer when we consider the dark fringes in a single slit experiment,all the rays in each of the slits are cancelled leaving no rays for further superposition,in case of secondary maxima,we are left with some rays,are those rays actually superpose to give rise to the interference with in the two slits. – sachin Mar 21 '19 at 16:57
• @sachin You can also derive the interference pattern from individual photons. – Bill Alsept Mar 21 '19 at 18:08