A travelling wave transfers energy through space, whereas a standing wave has a fixed pattern of nodes and antinodes with no net energy transfer along the medium. This distinction is part of IB Physics C.4, Standing waves and resonance, and applies to both SL and HL.
A travelling wave moves through a medium or through space. Each point oscillates with the same frequency, but points at different positions generally have different phases. For an ideal wave without attenuation, every point has the same amplitude.
A standing wave forms through the superposition of two identical travelling waves moving in opposite directions. They must have the same frequency, wavelength and amplitude. Their interference produces fixed nodes, where the amplitude is zero, and fixed antinodes, where the amplitude is maximum.
| Feature | Travelling wave | Standing wave |
|---|---|---|
| Pattern | Travels through space | Remains fixed in position |
| Energy | Transfers energy in the direction of propagation | Has no net energy transfer along the medium |
| Amplitude | Ideally equal at all positions | Changes with position from zero to maximum |
| Special points | No permanent nodes or antinodes | Fixed nodes and antinodes |
| Phase | Changes continuously with position | Points between adjacent nodes oscillate in phase; neighbouring segments oscillate in antiphase |
| Wavelength measurement | Distance between adjacent points in phase | Adjacent nodes are separated by ; a node and adjacent antinode by |
