General Properties of WavesOxford AQA IGCSE Physics: Revision notes
Section 1
What is a wave?
A wave is a disturbance caused by an oscillating source that transfers energy and information without transferring matter.
This is a key idea: when a wave passes through water, air, or a solid, the particles of the medium oscillate but do not travel along with the wave — only energy and information move from one place to another.
A very common exam error is saying waves transfer matter. Always state clearly that waves transfer energy and information, not matter.
Section 2
What is the difference between transverse and longitudinal waves?
| Feature | Transverse | Longitudinal |
|---|---|---|
| Direction of oscillation | Perpendicular to direction of energy transfer | Parallel to direction of energy transfer |
| Examples | Electromagnetic waves, water waves | Sound waves |
| Pattern | Peaks and troughs | Compressions and rarefactions |
Mechanical waves (waves that travel through a physical medium) may be either transverse or longitudinal, depending on the type.
- Electromagnetic waves and water waves are transverse
- Sound waves are longitudinal
Section 3
What happens when a wave meets a boundary?
When a wave reaches the boundary between two different materials, it can be:
- Reflected — bounced back from the boundary
- Transmitted — passes through into the new material, often refracting
- Absorbed — the wave's energy is taken in by the material
Refraction is the change in velocity (and usually direction) of a wave as it crosses a boundary between two materials.
Diffraction is the spreading out of a wave as it passes through a narrow gap or travels past an edge.
Section 4
How are waves described and measured?
Key wave properties:
- Frequency — the number of complete waves passing a point per second, measured in hertz (Hz)
- Wavelength — the distance from one point on a wave to the identical point on the next wave (e.g. crest to crest)
- Period — the time taken for one complete wave to pass a point
- Amplitude — the maximum displacement of a point on the wave from its undisturbed (rest) position
- Wavefront — a line or surface representing points on a wave that are in phase (e.g. all at a crest at the same moment)
Section 5
How do you calculate wave speed?
Wave speed is calculated using:
v = f × λ
- v = wave speed (metres per second)
- f = frequency (hertz)
- λ = wavelength (metres)
This equation applies to all types of waves, transverse and longitudinal.
A wave has a frequency of 50 Hz and a wavelength of 2 m. Its speed is v = f × λ = 50 × 2 = 100 m/s.
Must Know
- A wave is a disturbance from an oscillating source that transfers energy and information, not matter
- Transverse waves oscillate perpendicular to energy transfer (EM waves, water waves); longitudinal waves oscillate parallel to energy transfer, with compressions and rarefactions (sound waves)
- Waves can be reflected, transmitted or absorbed at a boundary; refraction is a change in velocity/direction; diffraction is spreading through a gap or past an edge
- Frequency, wavelength, period, amplitude and wavefront are the key measurable properties of a wave
- Wave speed: v = f × λ
That's the notes covered.
Carry on to the next subtopic.