Lesson focus: waveA movement that carries energy from one place to another without carrying the material with it, like a ripple on a pond. transfer energy and information while the material carrying a mechanical wave only oscillates around its equilibrium position.
Compare transverseDescribes a wave, like a water ripple, where the up-and-down movement is at right angles to the direction the wave travels. and longitudinalDescribes a wave, like sound, where the particles move back and forth in the same direction the wave travels. and identify amplitudeThe height of a wave from the middle line to the top of a peak; bigger amplitude means a louder sound., wavelengthThe distance from one point on a wave to the same point on the next wave, such as peak to peak. and frequencyHow many times something happens each second; for a wave, how many waves pass each second, measured in hertz (Hz). from models.
Build on earlier learning
Laboratory equipmentYear 7 developed careful measurement from scales. This lesson applies that precision to wave amplitude, wavelength and frequency.
You will be successful when you can…
- Define a wave as an energy-transfer process.
- Distinguish transverse from longitudinal waves using vibration direction.
- Identify amplitude, wavelength, compression and rarefaction.
- Evaluate what a wave model represents and what it leaves out.
Words that carry the science
- wave
- A travelling disturbance that transfers energy and can carry information without net transfer of matter.
- transverse
- A wave whose vibrations are perpendicular to the direction of energy transfer.
- longitudinal
- A wave whose vibrations are parallel to the direction of energy transfer.
- amplitude
- The maximum displacement from the equilibrium position.
- wavelength
- The shortest distance between two points in phase, such as crest to next crest.
- frequency
- The number of complete cycles passing a point each second, measured in hertz.
Separate wave travel from particle motion
01A wave transfers energy, not a stream of matter
A waveA movement that carries energy from one place to another without carrying the material with it, like a ripple on a pond. is a travelling disturbance. It can transfer energy and information from a source to a receiver while particles of a mechanical medium oscillate around their usual positions.
A floating marker may bob as a water waveA movement that carries energy from one place to another without carrying the material with it, like a ripple on a pond. passes, but it does not travel forward with every crest. This distinction prevents the common mistake that the water itself moves across the whole tank with the wave.
02Vibration direction identifies the wave type
In a transverseDescribes a wave, like a water ripple, where the up-and-down movement is at right angles to the direction the wave travels., vibration is at right angles to energy transfer. Light is transverseDescribes a wave, like a water ripple, where the up-and-down movement is at right angles to the direction the wave travels.. In a longitudinalDescribes a wave, like sound, where the particles move back and forth in the same direction the wave travels., vibration is parallel to energy transfer. Sound in air is longitudinalDescribes a wave, like sound, where the particles move back and forth in the same direction the wave travels..
Longitudinal waves contain compressionA part of a sound wave where the particles are squashed closer together., where particles are closer together than average, and rarefactionA part of a sound wave where the particles are spread further apart., where they are farther apart. Both regions travel even though each particle only moves locally.
03Wave quantities describe repeating structure
amplitudeThe height of a wave from the middle line to the top of a peak; bigger amplitude means a louder sound. is measured from equilibrium to a crest or trough, not crest to trough. wavelengthThe distance from one point on a wave to the same point on the next wave, such as peak to peak. connects equivalent neighbouring points, and frequencyHow many times something happens each second; for a wave, how many waves pass each second, measured in hertz (Hz). counts complete cycles per second.
These quantities describe a model under stated conditions. A larger amplitudeThe height of a wave from the middle line to the top of a peak; bigger amplitude means a louder sound. means more energy in otherwise comparable waves, while frequencyHow many times something happens each second; for a wave, how many waves pass each second, measured in hertz (Hz). and wavelengthThe distance from one point on a wave to the same point on the next wave, such as peak to peak. must not be treated as the same measurement.
Transverse waves
The water moves up and down while the wave travels along. Energy is transferred, not the water itself.
Controls
The speed is set by the water, so a higher frequency gives a shorter wavelength.
Classify a slinky disturbance
A pulse travels right along a slinky while each coil moves briefly left and right. Classify the wave.
- Mark the direction of energy transfer as right.
- Mark the coil vibration as left and right along the slinky.
- Compare the directions: they are parallel.
- Identify the regions of closer and wider coil spacing as compressions and rarefactions.
How to make the reasoning visible: The pulse is longitudinal because coil vibration is parallel to energy transfer.
Interrogate four wave models
Treat each model as evidence. Decide the vibration direction and state one limitation rather than judging only by appearance.
| Model | Vibration | Energy transfer | Best classification |
|---|---|---|---|
| Rope pulse | Up and down | Along the rope | Transverse |
| Slinky compression | Along the slinky | Along the slinky | Longitudinal |
| Light ray model | Electric and magnetic fields across travel direction | Along the ray | Transverse |
| Stadium wave | People stand and sit | Around the stadium | Transverse analogy |
Why is the stadium wave useful but incomplete as a model?
A diagram has a crest-to-trough height of 12 cm. What is its amplitude?
Check your understanding
Answer from memory, then check against the suggested answer.
What does a wave transfer?
How are vibration and travel directions related in a transverse wave?
What is measured in hertz?
A buoy rises and falls six times in three seconds as waves move past. Calculate the frequency.
Explain why a longitudinal wave can be drawn as a curve even though particles do not move up and down.
Exam Question Practice
Exam Question Practice
Mark points shown after marking
Waves can be transverse or longitudinal.
Compare transverse and longitudinal waves. Include what they transfer and the direction of the vibrations.
(3)Give one example of each type of wave.
(1)Total for this question: 4 marks
Command word: For compareA command word: say how two or more things are similar and how they are different., include a similarity and linked differences using the same feature.