3 Diffraction
Feynman Lectures, Volume III, Chapter I.
Gasciorawicz does not really this.
Rohlf Chapters 5
Griffiths doesn’t cover this.
3.1 Diffraction from Two Slits
Water waveswill exhibit a diffractive interference pattern in a 2 slit experiment as diagrammed
below. The diagram shows the crests of the water waves at some time. Downstream from the slits,
we will see constructive interference where the waves from the slits are in phase and destructive
interference where they are 180 degrees out of phase, for example where a crest from one slit meets
a trough from the other. The plot labeledI 12 shows the interference pattern at the location of the
absorber.Diffraction is a simple wave phenomenon.
Thediffraction of lightwas a well known phenomenon by the end of the 19th century and was well
explained in classical ElectroMagnetic theory since light was held to bea EM wave. The diffraction
pattern from two narrow slits is particularly easy to understand in terms of waves. The setup is
shown in the diagram below.