In deriving the single slit diffraction pattern, it was stated that the intensity is zero at angles of nλ/a. Justify this by suitably dividing the slit to bring out the cancellation.

The path difference between the beams at each ends of the slits can be written as

bsinθ = nλ


b is the size of the slit,

n is the order of the minima

θ is the phase angle.

The observations state that the intensity is zero at

First, Let us divide the slit into two equal parts. Then a path a difference of λ/2 i.e. π is introduced between the waves of each part. The waves then superimpose to interfere destructively and thus producing a zero intensity minima on the screen. We can thus observe the same results if we divide the screen accordingly for n = 2,3,4….