Interference
The phenomenon where two or more waves superpose, resulting in a combined wave pattern. Constructive interference occurs when waves are in phase (maxima align), amplifying the result. Destructive interference occurs when waves are 180° out of phase, cancelling out. The intensity pattern depends on path difference.
Formula
Constructive: path difference = nλ; Destructive: path difference = (n + ½)λ
Real World
Noise-cancelling headphones (such as Sony WH-1000XM5) use destructive interference — a microphone samples ambient noise and the speaker emits a wave 180° out of phase to cancel it.
Exam Focus
Always express path difference in terms of wavelength; quoting it in metres without relating to λ will not score the mark.
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