How a Stationary Wave Forms
How a Stationary Wave Forms
- Send a wave towards a boundary. Its reflection travels back through the incoming wave.
- When the two waves have the same frequency, wavelength and amplitude but travel in opposite directions, their superposition can make a pattern that does not travel.
Two travelling waves make one fixed pattern
t = 0.15 T·pulse factor cos(ωt) = 0.59·pattern is at maximum displacement
- At some positions the waves always cancel. Those points never move.
- Halfway between them the waves repeatedly add to the greatest possible amplitude.
- The pattern alternates between its two extreme shapes, passing through a flat instant. The loops do not travel along the medium.
Definition
2 marksWhat is meant by a stationary wave?
Model answer: A wave pattern formed by the superposition of two waves of equal frequency and amplitude travelling in opposite directions.
Do not confuse it with a progressive wave
| Feature | Progressive wave | Stationary wave |
|---|---|---|
| energy transfer | energy is transferred | no net energy transfer along the pattern |
| amplitude | same in an ideal uniform medium | depends on position: zero at nodes, maximum at antinodes |
| phase | changes continuously with position | same within one loop; adjacent loops are in antiphase |
| pattern | travels | nodes and antinodes stay fixed |
Your turn9702-style
Explain how two progressive waves produce a stationary wave. [3]
Show worked answer
The waves have equal frequency, wavelength and amplitude, travel in opposite directions, and superpose. Their repeated constructive and destructive interference produces fixed antinodes and nodes.