AQA · A-Level · Physics
Course version: 7408 · Version from Sept 2016
Stationary waves formed on a string and those produced with microwaves and…
Full specification wording
Principle of superposition of waves and formation of stationary waves: Stationary waves formed on a string and those produced with microwaves and sound waves should be considered.
Stationary waves appear in several practical situations.
Checked against the AQA 7408 specification (opens in a new tab) on .
- Point 5 of 7
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
Stationary waves appear in several practical situations. On a stretched string, a wave reflects at a fixed end and interferes with the incident wave; nodes occur at fixed ends and antinodes at free positions, and the string can vibrate in harmonics. With microwaves, a transmitter directs waves at a metal reflector; the reflected wave superposes with the incident wave, producing nodes and antinodes that can be detected with a probe. With sound waves, a loudspeaker facing a hard surface or a resonance tube creates stationary waves; nodes and antinodes in air can be located using a microphone or by resonance. In each case, the same physics applies: same frequency, opposite directions, superposition, and a pattern with fixed nodes and antinodes.
What earns the marks
- Describe how a stationary wave forms on a stretched string by reflection at a fixed end and superposition with the incident wave.
- State that nodes occur at fixed ends of a string and antinodes occur at positions of maximum vibration.
- Describe how microwaves from a transmitter reflect from a metal plate and form a stationary wave detected by a probe.
- Describe how sound waves from a loudspeaker reflect from a hard surface or within a tube to form a stationary wave.
- Identify that in all three cases the stationary wave has the same frequency as the source and a node spacing of half a wavelength.
- Explain how measurements of node or antinode positions can be used to determine wavelength.
Common mistakes and how to put them right
Believing that a stationary wave transfers energy along the string or through the air.
Put it right by stating that energy is stored in the oscillating system and not propagated.
Thinking that nodes are always at the ends of every medium.
Put it right by noting that nodes occur at fixed boundaries, while free ends or open tube ends may be antinodes.
Assuming microwaves and sound waves cannot form stationary waves because they are not visible.
Put it right by explaining that any wave reflecting and superposing can form stationary waves.
Exam tips
- For each example, state the wave source, the reflector, and how nodes and antinodes are detected or observed.
- Use the node spacing to calculate wavelength, remembering that adjacent nodes are separated by half a wavelength.
- Compare the three examples in a table to show the common physics and the different detection methods.
Try the lesson
The start of the Principle of superposition of waves and formation of stationary waves: Stationary waves formed on a string and those produced with microwaves and sound waves should be considered. lesson, made from checked teaching notes for this specification point.
Have a go first
A stationary wave is set up on a stretched string fixed at both ends. What is always found at each fixed end of the string?
Listen
Stationary waves appear in several practical situations. On a stretched string, a wave reflects at a fixed end and interferes with the incident wave; nodes occur at fixed ends and antinodes at free positions, and the string can vibrate in harmonics. With microwaves, a transmitter directs waves at a metal reflector; the reflected wave superposes with the incident wave, producing nodes and antinodes that can be detected with a probe. With sound waves, a loudspeaker facing a hard surface or a resonance tube creates stationary waves; nodes and antinodes in air can be located using a microphone or by resonance. In each case, the same physics applies: same frequency, opposite directions, superposition, and a pattern with fixed nodes and antinodes. A strong answer earns marks for these points. Describe how a stationary wave forms on a stretched string by reflection at a fixed end and superposition with the incident wave. State that nodes occur at fixed ends of a string and antinodes occur at positions of maximum vibration. Describe how microwaves from a transmitter reflect from a metal plate and form a stationary wave detected by a probe. Describe how sound waves from a loudspeaker reflect from a hard surface or within a tube to form a stationary wave. A common slip: Believing that a stationary wave transfers energy along the string or through the air. Instead, stating that energy is stored in the oscillating system and not propagated. Exam tip: For each example, state the wave source, the reflector, and how nodes and antinodes are detected or observed.
See it
Put it in order
Put these steps in the order they happen.
- 1. Superposition of incident and reflected waves
- 2. Node spacing of half a wavelength used to determine wavelength
- 3. Stationary wave with fixed nodes and antinodes
- 4. Wave source
- 5. Incident wave travels towards reflector
- 6. Nodes and antinodes detected or observed
- 7. Reflection at fixed end, metal plate or hard surface
- 8. Reflected wave travels in opposite direction
Key words
Say what each word means before you turn the card.
Stationary waves on strings
Try answering aloud or in your head before turning the card.
Microwave stationary waves
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Sound stationary waves
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Wavelength measurement
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See every definition
- Stationary waves on strings
- A wave reflects at a fixed end and interferes with the incident wave, with nodes at fixed ends and antinodes at free positions, and the string can vibrate in harmonics.
- Microwave stationary waves
- A transmitter directs waves at a metal reflector and the reflected wave superposes with the incident wave, producing nodes and antinodes that can be detected with a probe.
- Sound stationary waves
- A loudspeaker facing a hard surface or a resonance tube creates them, and nodes and antinodes in air can be located using a microphone or by resonance.
- Wavelength measurement
- Measurements of node or antinode positions can be used to determine wavelength, with a node spacing of half a wavelength.
Label the diagram
Some boxes have lost their names. Pick the right name for each number.
1Box 1
2Box 2
3Box 3
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