P3.1P3. Waves

General properties of waves — Combined Science 0653 - Physics Revision Notes & Topical Questions

5 min read 10 parts Lesson 2 of 9 1 quiz

📚 Combined Science 0653 - Physics Hub / Topical Revision

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Lesson summary

P3.1 General properties of waves — COMBINED SCIENCE notes: Describe wave features, use v = fλ and f = 1/T, distinguish transverse from longitudinal waves, and describe reflection, refraction and diffraction.Wave = an oscillation or vibration about a fixed point that transfers ene…

Observing waves
Amplitude (A)
Wavelength (λ)
Frequency (f)
Crest (peak)
Wave speed (v)

Part 1 of 8Waves and energy transfer

Wave

Wave an oscillation or vibration about a fixed point that transfers energy without transferring matter.

Evidence

Evidence an object floating on water bobs up and down but does not travel with the wave.

Examples

Examples ripples make water particles oscillate up and down, and sound makes air particles vibrate back and forth.

Observing waves

Observing waves vibrations in ropes and springs, and water waves in a ripple tank, show wave properties.

Part 2 of 8Features of a wave

Features of a wave

Wavefront

Wavefront a line joining points on a wave that are in step, usually the crests, seen from above.

The direction of travel is shown by a ray at right angles to the wavefronts.
The gap between wavefronts is the wavelength.

Amplitude (A)

Amplitude (A) the maximum displacement of a wave from its undisturbed position, measured in metres.

It is measured from the rest position to a crest or trough, not from crest to trough.

Wavelength (λ)

Wavelength (λ) the distance from one point on a wave to the same point on the next wave, in metres.

In a transverse wave it is crest to crest, and in a longitudinal wave it is compression centre to compression centre.

Frequency (f)

Frequency (f) the number of waves passing a point per second, in hertz (Hz).

Crest (peak)

Crest (peak) the highest point of a wave above its undisturbed position.

Trough

Trough the lowest point of a wave below its undisturbed position.

Wave speed (v)

Wave speed (v) the distance travelled by a wave each second, in m/s.

Part 3 of 8Wave equation and period

Wave equation

Wave equation v = f × λ, with v in m/s, f in Hz and λ in m.
What the symbols mean: v = wave speed (m s⁻¹) · f = frequency (Hz) · λ = wavelength (m)
It applies to both transverse and longitudinal waves.

Period (T)

Period (T) the time taken for one complete wave to pass a fixed point.

Link

Link f = 1 ÷ T and T = 1 ÷ f, with T in seconds.

Speed from distance

Speed from distance v = d ÷ t for the distance a wave pulse travels.

Fixed speed

Fixed speed a higher frequency means a shorter wavelength.

Part 4 of 8Transverse and longitudinal waves

Property	Transverse	Longitudinal
Vibration	At right angles to the direction of travel	Parallel to the direction of travel
Structure	Crests and troughs	Compressions and rarefactions
Vacuum	Only electromagnetic waves can travel through it	Cannot travel through it
Media	Solids and the surface of liquids for mechanical waves	Solids, liquids and gases
Pressure and density	Constant	Vary along the wave
Examples	Light and all electromagnetic waves, water ripples, waves on a rope, seismic S-waves	Sound, seismic P-waves, waves on a slinky

Compression

Compression a region where particles are close together and the pressure is high.

Rarefaction

Rarefaction a region where particles are spread apart and the pressure is low.

Part 5 of 8Reflection, refraction and diffraction

Medium

Medium the material a wave travels through, and several are called media.

All waves

All waves transverse and longitudinal waves can all be reflected, refracted and diffracted.

Reflection

Reflection a wave bounces back at a boundary and stays in the original medium.

Angle of incidence = angle of reflection, measured from the normal.
Speed, wavelength and frequency do not change.

Refraction

Refraction a change in the speed of a wave when it crosses a boundary between two media.

The speed, wavelength and direction change, but the frequency does not.
A wave that slows down bunches up, so its wavelength decreases and it turns towards the normal.
A wave that speeds up spreads out, so its wavelength increases and it turns away from the normal.

Diffraction

Diffraction the spreading out of waves as they pass through a gap or around an edge, with no change in wavelength.

Part 6 of 8Factors affecting diffraction

Gap width

Gap width diffraction is greatest when the gap is about the same size as the wavelength.

Wide gap

Wide gap as the gap gets much wider than the wavelength, the waves hardly spread and only the edges curve.

Wavelength

Wavelength longer wavelengths diffract more around gaps and edges.

Everyday evidence

Everyday evidence long-wavelength radio waves bend round hills and long-wavelength sound bends round corners,
- but light with a tiny wavelength does not.

Part 7 of 8Investigating waves in a ripple tank

Fill a shallow, level tank with water and fit a vibrating straight bar (dipper) driven by a motor to make plane waves.

Shine a lamp above the tank so the wavefronts show as bright and dark lines on a screen below.

For reflection, place a metal bar at an angle and compare the angles of the incident and reflected wavefronts.

For refraction, place a glass block under the water so that the water over it is shallow, and watch the waves slow down and the wavelength shorten.

For diffraction, place barriers to make a gap or an edge and change the gap width or the motor frequency.

Motor frequency

Motor frequency a higher frequency gives a shorter wavelength and a lower frequency gives a longer wavelength.

Depth

Depth waves travel more slowly in shallow water.

Part 8 of 8More from the specification

Key terms

Term	Meaning
Wavelength	The distance between the same points on two neighbouring waves.
Frequency	The number of waves passing a point per second, in hertz.
Amplitude	The maximum displacement of a wave from its undisturbed position.
Wavefront	A line joining points on a wave that are in step.
Transverse wave	A wave whose vibrations are at right angles to the direction of travel.
Longitudinal wave	A wave whose vibrations are parallel to the direction of travel.
Compression	A region of a longitudinal wave where particles are close together.
Rarefaction	A region of a longitudinal wave where particles are spread apart.
Diffraction	The spreading of waves as they pass through a gap or round an edge.

Avoid these mistakes

Measuring amplitude from crest to trough — amplitude is measured from the rest position to a crest or trough.

Saying the frequency changes when a wave refracts — it stays the same, only speed and wavelength change.

Saying a wave carries matter along with it — it transfers energy only.

Saying sound can travel through a vacuum — it is longitudinal and needs a medium.

Saying diffraction changes the wavelength — the wavelength stays the same.

Last updated: 15 October 2026