Electromagnetic spectrum
The order of the spectrum, common uses and the dangers of each region.
Review these first
Learning objectives
What you need to be able to do
Teacher-mapped phrasing — check against the official Cambridge syllabus for exact wording.
- 3.3.1State the regions of the electromagnetic spectrum in order of wavelength and frequency.
- 3.3.2Describe typical uses and hazards of each region.
- 3.3.3State that all electromagnetic waves travel at the same speed in a vacuum, 3.0 × 10⁸ m/s.
6 minute read
The electromagnetic spectrum
The electromagnetic spectrum is a continuous family of transverse waves, all travelling at the same speed in a vacuum — 3.0 × 10⁸ m/s — but with different wavelengths and frequencies. In order of increasing frequency (decreasing wavelength):
Radio → Microwave → Infrared → Visible light → Ultraviolet → X-ray → Gamma
A useful memory device: "Rabbits Mate In Very Unusual eXtreme Gardens" gives the same order.
Uses
- Radio waves: broadcasting, communications.
- Microwaves: satellite communication, cooking (heating water molecules in food).
- Infrared: thermal imaging, remote controls, cooking (grills), fibre-optic communication.
- Visible light: vision, photography, fibre-optic communication.
- Ultraviolet: sunbeds, fluorescent lamps, security marking (invisible ink visible under UV).
- X-rays: medical imaging of bones, airport security scanning.
- Gamma rays: sterilising medical equipment, treating cancer.
Hazards
As frequency increases, the waves carry more energy and generally become more dangerous to living tissue. Ultraviolet can cause skin damage and eye damage; X-rays and gamma rays are ionising — they can damage or mutate cells and DNA, causing cancer, so exposure is minimised with lead shielding and short exposure times.
Think of it like this
The electromagnetic spectrum is like one musical instrument playing notes across an enormous range — radio waves are the lowest, slowest "notes" and gamma rays the highest, fastest, most energetic ones, but they are all fundamentally the same kind of wave.
Worked examples
Method, step by step
A radio wave has a frequency of 1.5 × 10⁶ Hz. Calculate its wavelength.
- 1v = fλ, so λ = v / f
- 2λ = (3.0 × 10⁸) / (1.5 × 10⁶)
λ = 200 m
Common misconceptions
- Thinking different regions of the spectrum travel at different speeds in a vacuum. They are all 3.0 × 10⁸ m/s in a vacuum; only their wavelength and frequency differ.
- Assuming only gamma rays and X-rays are electromagnetic waves. Visible light, radio waves and all the others are equally part of the same spectrum, just at different frequencies.
- Believing infrared and ultraviolet are visible. Both lie just outside the range the human eye can detect.
In the exam
- Learn the order both ways — by increasing wavelength and by increasing frequency — since questions ask for either.
- When asked for a hazard, name the specific effect (e.g. "UV causes skin cancer/premature ageing", "X-rays and gamma rays are ionising and can cause cancer/cell damage"), not just "it is dangerous".