The electromagnetic spectrum
What it is
The electromagnetic (EM) spectrum is a continuous family of transverse waves that all travel at the same speed in a vacuum: c = 3 × 10⁸ m/s. They differ in wavelength (λ) and frequency (f) related by c = f λ. EM waves do not need a medium and can pass through space.
Order — long λ to short λ
Radio → Microwave → Infrared → Visible → Ultraviolet → X-ray → Gamma
Mnemonic: "Roman Men Invented Very Unusual X-ray Guns".
As wavelength decreases, frequency and energy per photon both increase. Higher-frequency waves are more dangerous because they carry more energy.
Uses (Edexcel-named)
| Wave | Use |
|---|---|
| Radio | TV / radio broadcast |
| Microwave | Cooking; satellite communications |
| Infrared | Heaters; remote controls; thermal imaging |
| Visible | Human vision; fibre-optic communication |
| Ultraviolet | Fluorescent lamps; tanning; security marker pens |
| X-ray | Medical imaging of bones |
| Gamma | Sterilising medical instruments; cancer treatment |
Hazards
- Microwaves — internal heating of body tissues.
- Infrared — skin burns.
- Ultraviolet — skin cancer, premature ageing, eye damage.
- X-ray and gamma — ionising; can cause cell mutation and cancer.
Risk depends on the dose (intensity × time) and on whether the radiation is ionising.
Generating and detecting EM waves (Higher)
EM waves are produced when charged particles oscillate or lose energy (e.g. electrons in an aerial). They can be absorbed, transmitted or reflected by matter; absorption may cause heating or generate an alternating current in a receiver.
AI-generated · claude-opus-4-7 · v3-edexcel-combined-science-leaves