Why in diffration value of n starts from 1 but not from zero as in interferance?d (sin) (theta)=n lambda ,where n=1,2,3,4....... so why value of n is not zero? plzz explain it

Dear student,

When we talk of interference, we want to find out points where there will be constructive interference, that is, maxima in the pattern. For n=0 , the path difference would be zero and it would give a constructive interference.

However in case of diffraction, the postitions of ‘minima’ are given by. If we put n=0, it would talk about the point of center of the screen where actually would be the maxima, not minima( due to no path difference from the diffracted light). Hence minima starts from n=1.