Stationary Waves
- Stationary waves, or standing waves, are produced by the superposition of two waves of the same frequency and amplitude travelling in opposite directions
- This is usually achieved by a travelling wave and its reflection
- The superposition produces a wave pattern where the peaks and troughs do not move
- Stationary waves store energy, unlike progressive waves which transfer energy
Formation of a stationary wave on a stretched spring fixed at one end
Comparing Progressive & Stationary Waves
Nodes & Antinodes
- A stationary wave is made up nodes and antinodes
- Nodes are regions where there is no vibration
- Antinodes are regions where the vibrations are at their maximum amplitude
- The nodes and antinodes do not move along the string
- Nodes are fixed and antinodes only move in the vertical direction
- The phase difference between two points on a stationary wave are either in phase or out of phase
- Points between nodes are in phase with each other
- Points that have an odd number of nodes between them are out of phase
- Points that have an even number of nodes between them are in phase
- The image below shows the nodes and antinodes on a snapshot of a stationary wave at a point in time
-
- Where:
- L is the length of the string
- One wavelength λ is only a portion of the length of the string
- Where:
Worked Example
A stretched string is used to demonstrate a stationary wave, as shown in the diagram.
Which row in the table correctly describes the length of L and the name of X and Y?
ANSWER: C
Exam Tip
Make sure you learn the definitions of node and antinode:
- Node = A point of minimum or no disturbance
- Antinode = A point of maximum amplitude
In exam questions, the lengths of the strings will only be in whole or half wavelengths. For example, a wavelength could be made up of 3 nodes and 2 antinodes or 2 nodes and 3 antinodes.
