A family of transverse waves
The electromagnetic (EM) spectrum is the full range of electromagnetic waves. Although their wavelengths differ enormously, they share important properties: they are all transverse waves, they can travel through a vacuum, and in a vacuum they all travel at the same speed — the speed of light, c = 3 × 10⁸ m/s.
Key idea
Wave speed v = f λ. For EM waves in a vacuum v = 3 × 10⁸ m/s, so higher frequency means shorter wavelength.
Order and uses
From longest wavelength (lowest frequency) to shortest wavelength (highest frequency):
| Radio | broadcasting, communication |
| Microwaves | cooking food, satellite & mobile signals |
| Infrared | remote controls, thermal imaging, heaters |
| Visible light | seeing, optical fibres, photography |
| Ultraviolet | fluorescent lamps, detecting forged notes, sterilising |
| X-rays | imaging bones, security scanners |
| Gamma rays | sterilising equipment, treating cancer |
Worked example
A radio wave has frequency 100 MHz (1 × 10⁸ Hz). Its wavelength λ = v ÷ f = (3 × 10⁸) ÷ (1 × 10⁸) = 3 m.
Remember
- Gamma rays and X-rays have the highest frequency and are the most dangerous (ionising).
- Excessive ultraviolet causes skin cancer and eye damage.
- All EM waves transfer energy without transferring matter.