Stationary wave
A wave pattern formed by the superposition of two progressive waves of equal frequency and amplitude travelling in opposite directions. Stationary waves have nodes (points of zero displacement) and antinodes (points of maximum displacement). No net energy travels along a stationary wave; the pattern is stationary in space.
Formula
Node spacing = λ/2
Real World
A guitar string fixed at both ends forms a stationary wave when plucked — the fixed ends are nodes and the string vibrates in segments, producing the note you hear.
Exam Focus
Identify nodes and antinodes on diagrams first, then count half-wavelengths to find the full wavelength.
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