Uses and applications of EM waves

Each part of the EM spectrum has applications based on its energy and how it interacts with matter.

Radio waves

• TV and radio broadcasting.
• Long-wave radio (low f, large λ) follows curves of Earth — broadcast over horizons.
• Short-wave reflects off ionosphere — long-distance.
• Microwaves: line-of-sight, satellite, mobile phones.

Microwaves

• Heating: water molecules absorb 2.45 GHz strongly — vibrate, transfer KE to surroundings.
• Mobile phones, satellite TV, radar.

Infrared

• Heating elements, remote controls, thermal imaging.
• Optical fibre communications (long-distance internet via IR pulses through glass fibres).
• Night vision (warm bodies emit IR).

Visible light

• Vision (the only EM band our eyes detect).
• Photography, fibre-optic communication (visible/IR).
• Lasers in CD/DVD/Blu-ray.

Ultraviolet

• Suntan and Vitamin D production (good, in moderation).
• Sterilisation of water and equipment.
• Fluorescent lamps, security marking, photolithography.

X-rays

• Medical imaging (bone visible because Ca absorbs X-rays).
• Security scanning of luggage.
• Industrial inspection.

Gamma rays

• Cancer radiotherapy (target tumour cells).
• Sterilisation of medical equipment, food.
• Diagnostic tracers.

Hazards summary

• UV: skin burns (sunburn), cataracts, skin cancer.
• X-rays/gamma: ionise tissue → DNA damage → cancer or radiation sickness.
• High-power microwave: internal heating burns.
• Even visible: very intense (lasers) damages retina.

Why each use matches the wave

• High f (UV+) → enough photon energy to damage DNA → also useful for therapy.
• Low f (radio) → can travel long distances, low energy per photon, less harmful.
• Visible chosen by evolution because the Sun emits most strongly there and atmosphere is transparent.