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
where,
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….
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