In deriving the single slit diffraction pattern, it was stated that the intensity is zero at angle `n lambda//a`. Justify this by suitable dividing the slit to bring out the cancellation.

Explanation

Let the slit be divided into `n` smaller slits each of width `a' = (a)/(n)`.
The angle `theta = (n lambda)/(a) = (n lambda)/(a'n) = (lambda)/(a')`
Therefore, each of the smaller slits would send zero intensity in the direction of `theta`. Hence for the entire single slit, intensity at angle `n lambda//a` would be zero.