📖 In-Depth Theory
Uses of Radio Waves and Microwaves
RADIO WAVES:
BROADCASTING: AM and FM radio, TV broadcasts — travel long distances, reflect off ionosphere.
COMMUNICATION: aircraft, ships, emergency services.
ASTRONOMY: radio telescopes detect radio waves from distant stars and galaxies.
MRI SCANNERS: radio waves + magnetic field → detailed images of soft tissue (no ionising radiation).
MICROWAVES:
MOBILE PHONES AND WIFI: short-range communication.
SATELLITE COMMUNICATION: microwaves pass through the atmosphere and ionosphere (radio waves reflect off ionosphere — limited for satellite use).
MICROWAVE OVENS: microwave frequency matches water molecules' resonance → absorbed → food heats from inside.
RADAR: detect aircraft, ships, weather systems — measure distance by timing reflection.
Uses of Infrared, Visible and Ultraviolet
INFRARED (IR):
HEATING: electric heaters, grills — absorbed by surfaces, converted to heat.
REMOTE CONTROLS: TV, DVD players — IR pulses carry coded signals.
FIBRE OPTICS: IR carried along optical fibres for high-speed internet.
NIGHT VISION CAMERAS: detect IR emitted by warm bodies — useful in darkness.
THERMAL IMAGING: medical, security, wildlife observation.
VISIBLE LIGHT:
PHOTOGRAPHY: cameras capture visible light.
FIBRE OPTICS: carries data as light pulses — basis of broadband internet.
PHOTOSYNTHESIS: plants absorb red and blue light.
LASERS: surgery, barcode scanners, DVD reading.
ULTRAVIOLET (UV):
STERILISATION: UV kills bacteria and viruses — used in hospitals and water treatment.
FLUORESCENCE: some materials emit visible light when absorbing UV — security markings, fluorescent lamps.
BLACK LIGHTS: detect forged bank notes (UV-reactive ink).
VITAMIN D PRODUCTION: skin produces vitamin D when exposed to UV.
Uses of X-rays and Gamma Rays
X-RAYS:
MEDICAL IMAGING: pass through soft tissue, absorbed by bone → shadow on film/detector.
CT SCANS: multiple X-ray beams → 3D image of internal structures.
AIRPORT SECURITY: luggage scanning — detect metal, explosives.
MATERIAL TESTING: checking for cracks in metal castings and welds.
GAMMA RAYS:
CANCER TREATMENT (radiotherapy): focused beams kill tumour cells.
ST ERILISATION of medical equipment: kills all microorganisms without heat.
FOOD IRRADIATION: kills bacteria in food → longer shelf life.
MEDICAL TRACERS: gamma-emitting radioisotopes injected → gamma camera detects distribution in body → reveals organ function.
THICKNESS MONITORING: detect gamma penetration through materials in manufacturing.
MATCHING APPLICATION TO WAVE TYPE:
The wave chosen matches its properties to the application:
Must penetrate enough → not be absorbed too quickly.
Must interact appropriately with the target material.
Hazard must be managed — ionising types minimised.
⚠️ Common Mistake
MRI scanners use RADIO WAVES (not X-rays) — they are safe for soft tissue imaging with no ionising radiation. X-rays are used for imaging BONE and dense structures. Also: microwaves for SATELLITE communication (pass through ionosphere); radio waves for BROADCAST (reflect off ionosphere).
📌 Key Note
Radio: broadcast, MRI. Microwave: satellites, phones, radar, cooking. IR: heating, remote controls, night vision, fibre optics. Visible: photography, fibre optics, photosynthesis. UV: sterilisation, fluorescence, vitamin D. X-ray: medical imaging, airport security, CT. Gamma: radiotherapy, sterilisation, tracers.
🎯 Test Yourself
Question 1 of 2
1. Why are microwaves used for satellite communications rather than radio waves?
Microwaves pass through the ionosphere — radio waves reflect off it, preventing them from reaching satellites in orbit
Satellites can only detect microwaves — their receivers are not compatible with radio waves
Radio waves are dangerous at high altitude — microwaves are safer for satellite use
Microwaves are more powerful — they reach greater distances than radio waves
2. UV light is used to sterilise medical equipment. Why is UV effective for this?
UV heats the equipment to high temperatures, killing microorganisms by heat
UV is absorbed by metal — heating the equipment surface to kill bacteria
UV converts oxygen to ozone, which then kills bacteria chemically
UV has enough energy to damage DNA in microorganisms — killing or inactivating bacteria and viruses