4PH1
Waves & The Electromagnetic Spectrum
Waves · 1 question type
Exam Frequency Analysis
Past paper frequency (2018 to 2024)
This topic accounts for approximately 14% of your exam marks.
stable
High
Stable14%
Wave equation (v = fλ), transverse vs longitudinal and EM spectrum properties tested consistently.
Band-by-band uses
| Band | Typical uses |
|---|---|
| Radio waves | Television and radio broadcasting; long-range two-way radio communication; air-traffic control |
| Microwaves | Mobile phone signals; Wi-Fi and Bluetooth; satellite communications and weather radar; heating food in a microwave oven |
| Infrared (IR) | Heating elements in toasters and grills; thermal-imaging cameras and night-vision goggles; television remote controls; short-range data links and optical fibres |
| Visible light | Sight; photography and video; visible-wavelength fibre-optic data transmission; lasers |
| Ultraviolet (UV) | Fluorescent strip lighting; security marks on banknotes that glow under UV; sterilising medical instruments and water supplies; producing vitamin D in skin |
| X-rays | Medical imaging of bones, teeth and dense tissues; airport security scanners; checking welds and pipework for cracks in industrial sites |
| Gamma rays | Sterilising surgical instruments and food without heating; treating cancer (radiotherapy); medical imaging using radioactive tracers (PET scans) |
Why each band suits its job
- Radio waves are absorbed only weakly by air and the ground, and pass through walls; that makes them ideal for long-range broadcasting
- Microwaves of certain frequencies are absorbed strongly by water molecules in food, transferring energy quickly to the water and heating the meal. Other microwave frequencies pass through the atmosphere and most weather, so they are used by mobile-phone and satellite networks
- Infrared is given off by anything warm (including human bodies), so cameras tuned to IR can see in the dark; the same waves can be aimed at heating elements where the goal is to deliver warmth quickly
- Visible light can be focused with simple lenses and detected by the eye and by silicon sensors, which is the basis of vision, photography and fibre-optic data
- Ultraviolet carries enough energy per photon to break some chemical bonds, which is why it can sterilise surfaces and make fluorescent inks glow in security applications
- X-rays are absorbed by dense materials such as bone but pass through soft tissue, producing a "shadow" image
- Gamma rays are the most energetic band, easily killing living cells, which is exactly what is wanted when sterilising equipment or targeting tumour cells in radiotherapy