W.1 Characterizing Waves
Understanding the properties of waves, including frequency, wavelength, period, and amplitude.
Questions to explore
- ? How does energy travel from one place to another without anything being carried along?
- ? What do a guitar string, a ripple and a sunbeam have in common?
💡 Key ideas, explained simply
🌊 What a wave actually does
A wave carries energy from place to place without moving the material along. Drop a stone in a pond: the ripple spreads outward, but a floating leaf just bobs up and down — it does not travel to the shore.
↔️ Transverse vs longitudinal
In a transverse wave the particles vibrate *at right angles* to the direction of travel — like light and water ripples.
In a longitudinal wave they vibrate *along* the direction of travel, making compressions and rarefactions — like sound.
Two types of wave
| Feature | Transverse | Longitudinal |
|---|---|---|
| Particle motion | Perpendicular to travel | Parallel to travel |
| Looks like | Crests and troughs | Compressions and rarefactions |
| Examples | Light, water, S-waves | Sound, P-waves |
📖 Key terms
- Wavelength
- Distance between two matching points (e.g. crest to crest), in metres.
- Frequency
- Number of waves passing per second, in hertz (Hz).
- Amplitude
- Maximum displacement from the middle — how much energy the wave carries.
- Period
- Time for one complete wave, .
- Wave speed
- How fast the wave travels, .
1 Key Formulas
✏️ Worked example
The wave equation
A wave has a frequency of and a wavelength of . Find its speed.
- 1
Write the formula
- 2
Substitute
v = 300 m/s. Rearrange the same formula to find f or λ when speed is given.
Interactive Lab
Standing Wave Lab
Change frequency and see wavelength, nodes and antinodes respond in real time.
📡 Physics around you
Your Wi-Fi, radio and phone all send information on waves. A higher frequency squeezes more data through — which is exactly why 5G (higher frequency) can be faster than older networks.
🎯 Nail it in the exam
Wave Equation and Graphs
The wave equation is used in almost every wave paper. You must be able to rearrange it: , .
From a displacement–time graph: measure the time for one complete cycle → period , then .
From a displacement–distance graph: measure the distance between two consecutive crests → wavelength .
Many ‘analyse’ questions give a graph and ask you to deduce the frequency or wavelength, then calculate speed using .
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Check graph axes: displacement–time gives period; displacement–distance gives wavelength.
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Speed of light (and all EM waves) in vacuum is – you may need to use this in calculations.
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Always write the wave equation before substituting values – this shows your reasoning.
Transverse vs Longitudinal – Exam Describe Questions
A classic 3‑mark ‘describe’ question: “Describe how you could demonstrate the difference between transverse and longitudinal waves using a slinky spring.”
Model answer:
- Stretch the slinky on the floor.
- For transverse: flick one end side‑to‑side. The coils move perpendicular to the direction the pulse travels.
- For longitudinal: push and pull one end. The coils move parallel to the direction of travel, showing compressions and rarefactions.
Diagrams are always helpful.
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Transverse waves: examples – ripples on water, all EM waves, S‑waves (earthquakes).
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Longitudinal waves: examples – sound, P‑waves.
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Polarisation is only possible with transverse waves – this can be an extension question.
🧠 Check your understanding
Tap an answer to see if you're right — and why.
Q1. What is the unit of frequency?
Q2. A wave has a frequency of 50 Hz and a wavelength of 6 meters. What is its velocity?
📝 Exam-style questions
Try each one, then reveal the model answer.