Investigate transverse and longitudinal waves, their properties, and explore the full electromagnetic spectrum from radio waves to gamma rays.
A wave is a disturbance that transfers energy from one place to another without transferring matter. The particles (or fields) through which the wave moves vibrate but do not travel with the wave — they return to their rest position after the wave passes.
| Type | Particle vibration direction | Examples |
|---|---|---|
| Transverse | Perpendicular (at right angles) to the direction the wave travels | Light, all EM waves, water surface waves, waves on a string |
| Longitudinal | Parallel (in the same direction) to the direction the wave travels — creates compressions and rarefactions | Sound waves, P-waves in earthquakes, sound in air |
In a longitudinal wave, regions where particles are bunched together are called compressions and regions where they are spread apart are called rarefactions.
| Property | Symbol | Definition | Unit |
|---|---|---|---|
| Amplitude | A | Maximum displacement of a particle from its rest position. Determines the energy (intensity) of the wave. | metres (m) |
| Wavelength | λ (lambda) | Distance between two identical consecutive points — e.g. crest to crest or trough to trough. | metres (m) |
| Frequency | f | Number of complete wave cycles passing a point per second. | Hertz (Hz) |
| Period | T | Time taken for one complete wave cycle. | seconds (s) |
| Wave speed | v | Distance travelled by the wave per second. | m/s |
A higher amplitude means more energy. A higher frequency means shorter wavelength (for a given wave speed). Period and frequency are reciprocals of each other.
Electromagnetic (EM) waves are transverse waves that consist of oscillating electric and magnetic fields at right angles to each other and to the direction of travel. Unlike sound, they do not need a medium to travel — they can move through a vacuum.
The EM spectrum is a continuous range ordered by frequency (or wavelength). From lowest frequency / longest wavelength to highest frequency / shortest wavelength:
| Type | Approx. wavelength | Frequency range | Applications |
|---|---|---|---|
| Radio waves | > 0.1 m | < 3 GHz | AM/FM broadcasting, TV, long-distance communication |
| Microwaves | 1 mm – 0.1 m | 3 GHz – 300 GHz | Microwave cooking, radar, satellite and mobile communication |
| Infrared (IR) | 700 nm – 1 mm | 300 GHz – 430 THz | Thermal cameras, TV remotes, night vision, heat lamps |
| Visible light | 400 nm – 700 nm | 430 THz – 750 THz | Human vision, photography, fibre optics |
| Ultraviolet (UV) | 10 nm – 400 nm | 750 THz – 30 PHz | Sterilisation, causing sunburn, fluorescence, vitamin D production |
| X-rays | 0.01 nm – 10 nm | 30 PHz – 30 EHz | Medical imaging, airport security screening, material analysis |
| Gamma rays (γ) | < 0.01 nm | > 30 EHz | Cancer radiotherapy, nuclear reactions, sterilising food/equipment |
Visible light occupies only a tiny portion of the EM spectrum. White light is a mixture of all colours (wavelengths). A prism or raindrop separates white light into the spectrum: red → orange → yellow → green → blue → indigo → violet (ROYGBIV) — red has the longest wavelength and lowest frequency; violet has the shortest wavelength and highest frequency in visible light.
Switch between Wave mode (animated transverse wave) and EM Spectrum mode (click or drag to explore each band).