Understanding Diffraction in a Double Slit Experiment

[elabed haidar]

i just don't understand diffraction in a double slit , ? how is it related to interference?? like if i want to find how many bright fringes within the central bright fringe of the diffraction envelope?
or how many bright fringes are found between the bright fringes of the first and second of diffraction? please with explanation and thank you

 

[chrisbaird]

Each slit has a finite size, so the waves coming out of the top and bottom of the same slit interfere to give you diffraction. So if you are including the effects of diffraction, you can think of a double-slit experiment really as a double-double-slit experiment, with two interference patterns layered on top of each other. The width of each slit is typically much smaller than the slit separation, so the one interference pattern being layered on the other is much broader.