Superposition & Interference
When waves overlap, their instantaneous displacements add. Interference is not a separate force—it is the pattern produced by ordinary superposition.
How can two waves share the same place without blocking each other?
In a linear medium, each wave contributes independently. At every point, the actual displacement is simply the algebraic sum of those contributions.
Phase determines whether the two contributions reinforce, partially cancel, or fully cancel at a given point.
Slide one wave through phase and watch the resultant change.
When equal-frequency waves arrive nearly in phase, crest aligns with crest and trough with trough, so the resultant amplitude grows.
When equal-amplitude waves differ by half a cycle, each crest aligns with a trough and the resultant can vanish locally.
Interference does not normally destroy the original waves. After overlapping, each component continues according to the medium's wave equation.
Equal frequency alone does not determine interference. Relative phase decides the alignment of peaks and troughs.
When path lengths differ, the phase difference can change from point to point, creating alternating maxima and minima.
For many waves, measured intensity scales with amplitude squared, so doubling amplitude can quadruple intensity.