The electromagnetic spectrum
All electromagnetic (EM) waves are transverse, travel at 3 x 10^8 m/s in a vacuum, and transfer energy without transferring matter. They are arranged by wavelength and frequency.
Order (long wavelength / low frequency to short wavelength / high frequency)
Radio - Microwaves - Infrared - Visible - Ultraviolet - X-rays - Gamma rays.
Mnemonic: "Roman Men Invented Very Unusual X-ray Guns".
Uses and hazards
| Type | Typical use | Hazard |
|---|---|---|
| Radio | TV / radio broadcasting | Negligible at normal intensities |
| Microwaves | Mobile phones, satellite TV, microwave ovens | Heating of body tissue |
| Infrared | TV remotes, thermal imaging, electric heaters | Skin burns |
| Visible | Sight, fibre-optic communication | High intensities damage retina |
| Ultraviolet | Sun-tan beds, fluorescent tubes, sterilisation | Skin cancer, premature ageing, eye damage |
| X-rays | Medical imaging of bones, airport security | Ionising — can cause cancer |
| Gamma | Cancer treatment, sterilising medical equipment | Ionising — cell damage, cancer |
Properties to remember
- All EM waves are transverse and travel at the same speed in a vacuum.
- Wave equation: v = f x lambda. As frequency rises, wavelength falls.
- Higher-frequency waves (UV, X-ray, gamma) carry more energy per photon — they ionise atoms and damage DNA.
WJEC exam tip
For "explain why X-rays are dangerous" answers, link the physics to the biology: "X-rays are ionising B1 so they can damage DNA in cells B1 which can lead to mutations and cancer B1." Three sentences, three marks.
AI-generated · claude-opus-4-7 · v3-wjec-combined-science-leaves