Waves (AQA GCSE Physics): Revision Notes
Waves
What are waves?
Waves carry energy and information from one place to another without moving matter. Think about dropping a ball into a pond - the ball bobs up and down, but the wave energy moves outwards across the water surface.
This is a crucial concept to understand: while we see waves moving through materials like water or air, the actual particles of that material don't travel with the wave. They simply vibrate in place as the energy passes through.
Wave properties
All waves can be described using these key measurements:
Frequency
- How many waves pass a point each second
- Measured in hertz (Hz)
- Higher frequency = more waves per second
Speed
- How fast the wave travels
- Measured in metres per second (m/s)
Wavelength
- The distance between two matching points on a wave
- For example, from one peak to the next peak
- Measured in metres
Amplitude
- The maximum distance a point moves from its normal position
Common Mistake Alert! Amplitude is measured from the middle line to the top (or bottom) - NOT the full distance from top to bottom. Many students incorrectly measure the full height of the wave as the amplitude.
Period
- The time taken for one complete wavelength to pass a point
- Measured in seconds
- Formula: where T is period and f is frequency
Types of waves
Longitudinal waves
In longitudinal waves, particles vibrate back and forth in the same direction as the wave travels.
Example: Sound Waves
When you speak or clap your hands:
- Air particles move backwards and forwards along the direction the sound is travelling
- This creates areas of compression (particles squashed together) and rarefaction (particles spread apart)
- Your ear detects these pressure changes as sound
Transverse waves
In transverse waves, particles move up and down or side to side - at right angles to the direction the wave travels.
Examples of Transverse Waves
Water ripples on a pond:
- The water particles move up and down
- But the wave energy travels across the surface horizontally
Electromagnetic waves (like light and radio waves):
- Electric and magnetic fields oscillate perpendicular to the direction of travel
- This includes visible light, X-rays, and radio signals
Key differences
| Longitudinal waves | Transverse waves |
|---|---|
| Particles move along the same direction as the wave | Particles move across (perpendicular to) the wave direction |
| Example: Sound waves | Examples: Water ripples, light waves |
Remember that it's the wave energy that travels, not the actual particles or material. The particles just vibrate in their positions while the energy moves through them.
Key Points to Remember:
- Waves transfer energy without moving matter
- Amplitude is from the middle to the peak, not the full height
- Longitudinal waves: particles vibrate along the wave direction (like sound)
- Transverse waves: particles vibrate across the wave direction (like water ripples)
- Use the formula to find the period from frequency