AQA · GCSE · Physics
Course version: 8463 · Version from Sept 2016
The amplitude of a wave is the maximum displacement of a point on a wave…
Full specification wording
Properties of waves: The amplitude of a wave is the maximum displacement of a point on a wave away from its undisturbed position.
Amplitude is measured from the undisturbed, or rest, position of the medium out to a crest, or down to a trough; it is the largest displacement any point reaches.
Checked against the AQA 8463 specification (opens in a new tab) on .
- Point 2 of 7
- 3 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
Amplitude is measured from the undisturbed, or rest, position of the medium out to a crest, or down to a trough; it is the largest displacement any point reaches. That means the vertical height from a crest to the neighbouring trough is twice the amplitude, a favourite trap in graph questions. On a displacement-distance or displacement-time graph, read the amplitude off the displacement axis from the centre line to the peak, taking care with the scale. Amplitude carries the energy of the wave: a larger amplitude sound wave is louder, and a larger amplitude light wave is brighter, while the frequency of the wave is entirely separate. Amplitude does not depend on frequency or wavelength, so a quiet high-pitched note has both a small amplitude and a short wavelength.
What earns the marks
- Amplitude being the maximum displacement of a point on the wave.
- Stating that it is measured from the undisturbed or rest position.
- Reading the amplitude from a graph using the displacement axis scale.
- Halving a crest-to-trough measurement to obtain the amplitude.
Common mistakes and how to put them right
Quoting the full crest-to-trough height as the amplitude.
Measuring the amplitude along the time or distance axis instead of the displacement axis.
Saying amplitude is the height of the wave without saying what it is measured from.
Assuming a larger amplitude also means a higher frequency.
Exam tips
- Draw the undisturbed line on the diagram first, then measure from it.
- Read the graph scale before you measure; each small square is rarely worth one unit.
- If asked for the amplitude from a crest-to-trough value, show the division by two in your working.
Try the lesson
The start of the Properties of waves: The amplitude of a wave is the maximum displacement of a point on a wave away from its undisturbed position. lesson, made from checked teaching notes for this specification point.
Have a go first
What does the amplitude of a wave measure?
Listen
Amplitude is measured from the undisturbed, or rest, position of the medium out to a crest, or down to a trough; it is the largest displacement any point reaches. That means the vertical height from a crest to the neighbouring trough is twice the amplitude, a favourite trap in graph questions. On a displacement-distance or displacement-time graph, read the amplitude off the displacement axis from the centre line to the peak, taking care with the scale. Amplitude carries the energy of the wave: a larger amplitude sound wave is louder, and a larger amplitude light wave is brighter, while the frequency of the wave is entirely separate. Amplitude does not depend on frequency or wavelength, so a quiet high-pitched note has both a small amplitude and a short wavelength. A strong answer earns marks for these points. amplitude being the maximum displacement of a point on the wave. stating that it is measured from the undisturbed or rest position. reading the amplitude from a graph using the displacement axis scale. halving a crest-to-trough measurement to obtain the amplitude. Exam tip: Draw the undisturbed line on the diagram first, then measure from it.
See it
Key words
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amplitude
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undisturbed position
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displacement
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See every definition
- amplitude
- The maximum displacement of a point on a wave away from its undisturbed position.
- undisturbed position
- The rest position of the medium from which displacement is measured out to a crest or down to a trough.
- displacement
- The distance of a point on a wave from its undisturbed position, read off the displacement axis of a graph.
Label the diagram
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