The electromagnetic spectrum · Grade 9
Light is one member of a family of electromagnetic waves. In order of increasing frequency they are radio waves, microwaves, infrared, visible light, ultraviolet, X-rays and gamma rays. All travel at 3.0 × 10⁸ m/s in a vacuum. Each has uses – from phones to cancer treatment – and the higher-frequency ones can be dangerous.
Key facts
- Order (low to high frequency): radio, microwave, infrared, visible, ultraviolet, X-ray, gamma. Wavelength goes the other way.
- All EM waves are transverse and travel at c = 3.0 × 10⁸ m/s in a vacuum: c = fλ.
- Uses: radio – broadcasting; microwaves – cooking, phones, satellites; infrared – remotes, thermal cameras; visible – sight, optical fibres; UV – sterilising, security marks; X-rays – imaging bones; gamma – sterilising, radiotherapy.
- UV, X-rays and gamma rays are ionising: they can damage cells and DNA.
- Photon energy is proportional to frequency (E = hf).
- Radar and signal timing: distance = c × time (÷ 2 for an echo).