Constructive & Destructive Interference
The phenomenon where overlapping coherent waves combine to reinforce (constructive) or cancel (destructive) each other's amplitude.
Governing formula
Path Diff ΔL = m λ (Constructive), ΔL = (m + ½) λ (Destructive)
SI unit
m
In depth
Constructive interference occurs when crest meets crest (in phase), doubling amplitude. Destructive interference occurs when crest meets trough (out of phase), canceling amplitude.
Examples in the real world
Iridescent colors on soap bubbles created by thin-film interference, or acoustic dead spots in uncalibrated auditoriums.