General properties of waves
Wave motion, wavefronts, energy transfer, wave quantities, wave speed, and transverse and longitudinal waves.
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Before you begin
Ripples on a pond and a pulse sent along a spring are waves: they carry energy from place to place without carrying the material with them. The lessons start by describing wave motion on ropes, springs and water, including wavefronts in a ripple tank, and sorting waves into transverse and longitudinal. They finish by measuring a wave by its amplitude, wavelength, period and frequency and using v = fλ.
Be comfortable with: SI prefixes, because wave calculations use ms, kHz and cm, and reading graphs.
Learning goals
- Describe wave generation by vibrating sources, ropes and springs
- Describe ripple-tank waves using wavefronts
- Explain that waves transfer energy
- Explain that wave energy transfer does not transfer matter
- Compare transverse and longitudinal waves and give examples
- Use amplitude, frequency and wavelength to describe wave motion
- Define and use wave speed and period and interpret wave graphs
- Recall and apply wave speed = frequency × wavelength
Syllabus statements covered
- describe what is meant by wave motion as illustrated by vibrations in ropes and springs and by waves in a ripple tank (including use of the term wavefront)
- show an understanding that waves transfer energy without transferring matter
- define and use the terms speed, frequency, wavelength, period and amplitude including graphical representation
- recall and apply the relationship speed of wave = frequency × wavelength to new situations or to solve related problems
- compare transverse and longitudinal waves and give suitable examples of each
Lessons
Work through them in order.
- Wave motion: transverse and longitudinal wavesDistinguish local vibration from wave travel, explain energy transfer and classify transverse and longitudinal waves.
- Wavefronts and ripple tanksExplain how a dipper makes water waves and use straight or circular wavefronts to show how they spread.
- Wave quantities and wave speedRead amplitude, wavelength, period and frequency from wave graphs, and use v = fλ to find a wave's speed, frequency or wavelength.
Practise and check
Or choose
Topic reference
Quick reference
| Idea | Relationship or meaning | Unit |
|---|---|---|
| amplitude | the maximum displacement from the rest position | m |
| wavelength, λ | the distance between neighbouring crests | m |
| period, T | the time for one complete wave, T = 1/f | s |
| frequency, f | the number of complete waves per second | Hz |
| wave speed | v = fλ | m/s |
| Wave | Vibrations compared with the direction of travel | Examples |
|---|---|---|
| transverse | at right angles | water waves, light, a rope shaken sideways |
| longitudinal | along the same line | sound, a spring pushed and pulled |
Core knowledge to remember
- Waves transfer energy without transferring matter.
- A wavefront is a line joining points on a wave that are in step, such as the crest of a water wave.
- In a transverse wave the vibrations are at right angles to the direction the wave travels; in a longitudinal wave they are along it.
- Speed of wave = frequency × wavelength.
Common mistakes
- Saying a wave carries the material of the medium along with it.
- Measuring amplitude from crest to trough instead of from the rest position.
- Measuring wavelength between a crest and the next trough. That is half a wavelength.
- Forgetting to change ms to s or kHz to Hz before using v = fλ or T = 1/f.