The Electromagnetic SpectrumOxford AQA IGCSE Physics: Revision notes
Section 1
What are electromagnetic waves?
Electromagnetic (EM) waves are transverse waves that transfer energy from a source to an absorber. Unlike sound, EM waves do not need a medium — they can travel through a vacuum (space).
All electromagnetic waves travel at the same speed through a vacuum, and together they form a continuous spectrum. Across the spectrum, wavelength ranges from about m to m. In order of increasing frequency and energy (and decreasing wavelength), the seven regions are:
- Radio waves
- Microwaves
- Infrared
- Visible light
- Ultraviolet
- X-rays
- Gamma rays
Learn the order radio → microwave → infrared → visible → ultraviolet → X-ray → gamma exactly — as frequency and energy increase, wavelength decreases.
Section 2
How do we see visible light?
Visible light is the only part of the EM spectrum that our eyes can detect. Within visible light, different wavelengths are seen by the eye as different colours, ranging from red (longest wavelength, lowest frequency) to violet (shortest wavelength, highest frequency).
Section 3
How do objects emit and absorb infrared radiation?
All objects emit and absorb infrared radiation, and the amount depends on both the surface and the temperature:
- Darker, matt surfaces are better absorbers and emitters of infrared radiation
- Lighter, shiny surfaces are poor absorbers and emitters, but good reflectors
- Hotter objects radiate more infrared overall, and at higher frequencies
This links to the idea of black-body radiation — the range of electromagnetic radiation emitted by an object because of its temperature.
A matt black saucepan absorbs and radiates heat more effectively than a shiny silver one, which is why some cookware is polished to reduce heat loss.
Section 4
What are the uses of each part of the spectrum?
| Region | Example uses |
|---|---|
| Radio waves | TV, radio, Bluetooth |
| Microwaves | Mobile phones, satellite TV |
| Infrared | Remote controls, night vision, heating |
| Visible light | Photography, fibre optic communications |
| Ultraviolet | Security marking |
| X-rays | Medical imaging |
| Gamma rays | Sterilising instruments, killing bacteria in food |
Section 5
What are the hazards of EM radiation?
Higher-frequency, higher-energy EM waves are more hazardous because they can damage living cells:
- Microwaves — heating of body tissue
- Infrared — skin burns
- Ultraviolet — skin cancer, blindness
- X-rays — cell damage
- Gamma rays — genetic mutations
Simple protection measures include limiting exposure time, using shielding (e.g. lead for X-rays, thick concrete for gamma), and wearing protective clothing such as sunscreen (UV) or lead aprons (X-rays).
Because high-energy ionising radiation (UV, X-rays, gamma rays) can damage cells and DNA, exposure to it must always be monitored and minimised.
X-rays specifically affect photographic film in the same way as light, are absorbed by dense material such as metal and bone, but are transmitted through healthy soft tissue. This makes them useful in CT scanning, diagnosing bone fractures, checking for dental problems, and in high doses, killing cancer cells.
Don't say EM radiation is only dangerous in high doses without naming which regions are ionising (UV, X-ray, gamma) — mark schemes want the specific hazard matched to the specific region.
Must Know
- EM waves are transverse waves that transfer energy from a source to an absorber and can travel through a vacuum
- All EM waves travel at the same speed in a vacuum, forming a continuous spectrum from radio waves to gamma rays (increasing frequency/energy, decreasing wavelength)
- Visible light is the only part detected by the eye; different wavelengths appear as different colours
- Darker, matt surfaces absorb/emit infrared better; lighter, shiny surfaces reflect better; hotter objects radiate more at higher frequencies
- Each region has specific practical uses (radio–TV/radio, microwave–phones, infrared–remotes, UV–security marking, X-ray–medical imaging, gamma–sterilising)
- Ionising radiation (UV, X-ray, gamma) is hazardous — causes skin cancer, cell damage or genetic mutations — and exposure must be monitored and minimised
- X-rays are absorbed by bone/metal but transmitted by soft tissue, making them useful for imaging fractures and CT scanning
That's the notes covered.
Carry on to the next subtopic.