📖 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 are more powerful — they reach greater distances 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
2. UV light is used to sterilise medical equipment. Why is UV effective for this?
UV has enough energy to damage DNA in microorganisms — killing or inactivating bacteria and viruses
UV is absorbed by metal — heating the equipment surface to kill bacteria
UV converts oxygen to ozone, which then kills bacteria chemically
UV heats the equipment to high temperatures, killing microorganisms by heat