SACE Stage 2 Physics — Light & Atoms 3.1

Two-Source Interference

Two coherent point sources radiate circular wavefronts that overlap. Where crests meet crests, the waves add — antinodes. Where crests meet troughs, they cancel — nodes. Path difference p = r₂ − r₁ is the hero: p = nλ gives constructive, p = (n+½)λ gives destructive.