With wide barriers, the wave moves straight forward.
With narrow openings, the wave spreads out behind the opening.
Constructive interference occurs where two crests overlap.
Destructive interference occurs where a crest overlap a trough.
Creating a Diffraction Pattern
An incident laser beam (a plane wave) shines on a screen with two slits.
Waves spread out behind each slit.
The two waves created overlap as they spread out behind the two slits. The two
overlapped waves interfere, resulting in a pattern of light and dark bands on a screen.
Constructive interference occurs with r a1d r di2fer by a whole number of wavelengths.
Destructive interference occurs when r an1 r dif2er by a whole number of wavelengths
plus half a wave