Applications of the EM spectrum

The EM spectrum has the same fundamental wave properties throughout, but each band is used for very different jobs. Edexcel expects students to match wave to use, justify the choice in physics, and identify hazards.

Radio waves

• Use: TV and radio broadcasting; long-distance communication; some medical scans (MRI uses radio frequency).
• Why: long wavelengths reflect off the ionosphere or diffract around hills, so they travel long distances and into buildings.

Microwaves

• Use: cooking food; satellite communications; mobile phones; Wi-Fi; some weather radar.
• Why for cooking: water molecules in food absorb microwaves at 2.45 GHz strongly → heating from the inside.
• Why for satellites: they pass through the atmosphere with little absorption.

Infrared

• Use: electric heaters; remote controls; thermal imaging cameras (security, search-and-rescue, medicine); fibre-optic communication; cooking grills.
• Why: absorbed by skin and food → heating. All warm objects emit IR.

Visible light

• Use: human vision; photography; fibre-optic communication; illumination.
• Why: the only band our eyes detect; transmits through glass with little loss.

Ultraviolet

• Use: sunbeds (cosmetic tanning); fluorescent lamps and security marks (UV detected by special pens); sterilisation of water and surfaces.
• Why for sterilisation: UV photons are energetic enough to break DNA in micro-organisms and kill them.
• Hazard: ionising at high doses → skin cancer, cataracts.

X-rays

• Use: medical imaging of bones (denser materials absorb X-rays more); airport security scanners; checking welds and pipelines (industrial radiography).
• Why: short wavelengths penetrate soft tissue but are absorbed by bone, giving clear contrast.
• Hazard: ionising — radiographers stand behind lead screens; patients are dosed minimally.

Gamma rays

• Use: sterilising medical instruments and food; radiotherapy (cancer treatment); medical tracers in PET scans.
• Why for radiotherapy: gamma rays kill cells, so a focused beam destroys tumours.
• Hazard: ionising — destroys healthy cells too if not focused.

Edexcel exam tip

When a question gives you a use and asks "name the type of EM radiation", justify by linking to a property: "infrared — because it heats objects" or "X-rays — because they pass through soft tissue but are absorbed by bone". Naming alone scores 1; the reason scores the second mark.