OCR · GCSE · Physics
Course version: J249 · Version from Sept 2018
Describe wave motion in terms of amplitude, wavelength, frequency and period
Full specification wording
Wave behaviour: describe wave motion in terms of amplitude, wavelength, frequency and period
Wave motion is described by four linked quantities.
Checked against the OCR J249 specification (opens in a new tab) on .
- Point 2 of 12
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
Wave motion is described by four linked quantities. Amplitude is the maximum displacement of a point from its rest position, measured in metres; a taller wave carries more energy. Wavelength is the distance between two matching points on consecutive waves, such as crest to crest, also in metres. Frequency is the number of complete waves passing a point each second, measured in hertz (Hz), so 5 Hz means five full oscillations per second. Period is the time for one complete wave to pass, measured in seconds, and it is the reciprocal of frequency: period = 1 ÷ frequency. A wave of frequency 4 Hz therefore has a period of 0.25 s. On a displacement–distance graph the amplitude is the height from the centre line and the wavelength is the crest-to-crest spacing; on a displacement–time graph the period is the time between matching points.
What earns the marks
- States that amplitude is the maximum displacement from the rest position and is measured in metres.
- Identifies wavelength as the distance between matching points on consecutive waves, such as crest to crest.
- Defines frequency as the number of complete waves passing a point per second, measured in hertz.
- Recognises that period is the time for one complete wave and equals 1 ÷ frequency.
- Selects the correct quantity when given a graph or a numerical value with its unit.
Common mistakes and how to put them right
Confuses amplitude with wavelength.
Put it right: Keep amplitude as the height from the centre line and wavelength as the horizontal spacing between waves.
Treats frequency and period as the same quantity.
Put it right: Period = 1 ÷ frequency, so a higher frequency gives a shorter period.
Measures wavelength from a trough to the next crest.
Put it right: Measure between two matching points, such as crest to crest.
Gives frequency in seconds.
Put it right: State frequency in hertz and period in seconds.
Exam tips
- Read the unit in the option or question first: hertz points to frequency, seconds to period, metres to amplitude or wavelength.
- Sketch a quick displacement–distance graph and label the height and the crest-to-crest gap before choosing.
- Check any reciprocal calculation, for example 1 ÷ 0.5 s = 2 Hz, so the period and frequency match.
Try the lesson
The start of the Wave behaviour: describe wave motion in terms of amplitude, wavelength, frequency and period lesson, made from checked teaching notes for this specification point.
Have a go first
On a displacement–distance graph of a transverse wave, what does the amplitude represent?
Listen
Wave motion is described by four linked quantities. Amplitude is the maximum displacement of a point from its rest position, measured in metres; a taller wave carries more energy. Wavelength is the distance between two matching points on consecutive waves, such as crest to crest, also in metres. Frequency is the number of complete waves passing a point each second, measured in hertz (Hz), so 5 Hz means five full oscillations per second. Period is the time for one complete wave to pass, measured in seconds, and it is the reciprocal of frequency: period = 1 ÷ frequency. A wave of frequency 4 Hz therefore has a period of 0.25 s. On a displacement–distance graph the amplitude is the height from the centre line and the wavelength is the crest-to-crest spacing; on a displacement–time graph the period is the time between matching points. A strong answer earns marks for these points. States that amplitude is the maximum displacement from the rest position and is measured in metres. Identifies wavelength as the distance between matching points on consecutive waves, such as crest to crest. Defines frequency as the number of complete waves passing a point per second, measured in hertz. Recognises that period is the time for one complete wave and equals 1 ÷ frequency. Exam tip: Read the unit in the option or question first: hertz points to frequency, seconds to period, metres to amplitude or wavelength.
See it
Key words
Say what each word means before you turn the card.
Amplitude
Try answering aloud or in your head before turning the card.
Wavelength
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Frequency
Try answering aloud or in your head before turning the card.
Period
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See every definition
- Amplitude
- The maximum displacement of a point from its rest position, measured in metres.
- Wavelength
- The distance between two matching points on consecutive waves, such as crest to crest, also in metres.
- Frequency
- The number of complete waves passing a point each second, measured in hertz.
- Period
- The time for one complete wave to pass, measured in seconds, and equal to 1 ÷ frequency.
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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