Question

State the conditions for secondary maximum and secondary minimum in diffraction pattern.​

Answer 1

Interference patterns from double-slits, multiple slits and diffraction gratings are different from single-slit diffraction patterns because the explanations of how the maxima and minima are formed are different.

Actually, double-slit interference patterns are combined with less obvious single-slit diffraction effects, as you might expect.

Anyway, the theory of double-slit interference is fairly straightforward and the explanation of multiple-slit patterns is just an extension of that. However, the theory of the patterns caused by single-slit diffraction is, I think, a bit harder to understand