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.

Consider that a single slit of width d is divided into n smaller slits.

Therefore, width of each slit,

d’ = d/n

Angle of diffraction is given by the relation,

0 = (d λ/d’) /d = λ/d’

Now, each of these infinitesimally small slit sends zero intensity in direction 0. Hence, the combination of these slits will give zero intensity.