Grade 8 · Waves, Light and Sound · Wave Behaviour
Properties of Waves
Amplitude, wavelength, frequency and the wave equation.
Learning objectives
- Label amplitude, wavelength and frequency on a wave.
- Compare transverse and longitudinal waves.
- Use the wave equation v = f x lambda.
NGSS alignment
HS-PS4-1
Use mathematical representations to support a claim regarding relationships among the frequency, wavelength, and speed of waves traveling in various media.
MS-PS4-1
Use mathematical representations to describe a simple model for waves that includes how the amplitude of a wave is related to the energy in a wave.
MYP criteria
- Criterion A — Knowing and Understanding
- Criterion C — Processing and Evaluating
ENGAGE
Feeling the bass
Standing near a speaker you can feel low notes in your chest, while high notes seem to come only from the speaker.
Think about it
- Which wave property changes between a low and a high note?
- What is actually travelling from the speaker to you?
EXPLAIN
Describing a wave
- Amplitude — maximum displacement from the rest position; linked to loudness or brightness
- Wavelength — distance between two matching points, measured in metres
- Frequency — waves per second, measured in hertz (Hz); linked to pitch or colour
- Period — time for one complete wave, equal to 1 / frequency
| Wave type | Vibration direction | Examples |
|---|---|---|
| Transverse | Perpendicular to travel | Light, water ripples, seismic S waves |
| Longitudinal | Parallel to travel | Sound, seismic P waves |
Wave equation
wave speed = frequency x wavelength, or v = f x lambda. A 250 Hz sound with wavelength 1.36 m travels at 340 m/s.
Careful
Waves transfer energy, not matter. Water in a ripple moves up and down; it does not travel across the pond.
Watch
Traveling Waves: Crash Course Physics
CrashCourse · 9 min
Explains amplitude, wavelength and frequency clearly.
Before you watch: What actually travels along a wave?
- State the wave equation.
- Compare transverse and longitudinal waves.
Interactive simulation · PhET
Waves Intro
Change the frequency and amplitude, then use the ruler and stopwatch to measure a wavelength.
While you explore
- What happens to wavelength when frequency increases?
- Which control changes amplitude only?
Key vocabulary
- Frequency
- How many waves pass each second.
- Wavelength
- The distance between one wave peak and the next.
Practice questions
0/2 correct
Level 1 · Criterion A
Which property of a sound wave determines its pitch?
Level 2 · Criterion A
A wave has frequency 50 Hz and wavelength 4 m. Its speed is:
MYP criterion tasks
Level 3 · Criterion C
A student measures 10 complete waves passing a point in 4.0 s and a wavelength of 0.6 m. Calculate the wave speed and comment on how to improve the measurement.
Reflect & track
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