Wave Interference
Superposition, standing waves, and double-slit patterns
When two waves overlap, they superpose: the total displacement at any point is the sum of individual displacements. If two crests meet, they add (constructive interference). If a crest meets a trough, they cancel (destructive interference). Standing waves form when reflected waves superpose with incident waves — nodes (zero displacement) and antinodes (maximum displacement) form at fixed positions. The double-slit experiment demonstrates that light (and matter) behaves as waves, with bright fringes where path lengths differ by whole wavelengths.
Can two sounds perfectly cancel each other out to create silence?
Noise-cancelling headphones do exactly this — they generate an inverted copy of ambient sound so the two waves destructively interfere, leaving near-silence.