Unit 12: Patterns in the Electromagnetic Spectrum
The electromagnetic (EM) spectrum shows a clear pattern: as wavelength decreases, frequency and energy increase. This unit explores that pattern and the uses of each type of EM wave.
01 The electromagnetic spectrum
All electromagnetic waves travel at the same speed in a vacuum (the speed of light, about 3 × 10⁸ m/s) but they have different wavelengths and frequencies. In order of increasing frequency (decreasing wavelength):
| Wave type | Common use |
|---|---|
| Radio waves | Broadcasting, communication |
| Microwaves | Cooking, satellite communication |
| Infrared | Heating, thermal cameras, remote controls |
| Visible light | Seeing, photography |
| Ultraviolet | Sterilising, sun tanning (and sunburn risk) |
| X-rays | Medical imaging of bones |
| Gamma rays | Cancer treatment, sterilising equipment |
02 The pattern: wavelength, frequency, energy
The pattern: as you move from radio waves to gamma rays, wavelength decreases, while frequency and energy increase. Higher-energy waves (like X-rays and gamma rays) can be more dangerous to living cells.
wave speed (m/s) = frequency (Hz) × wavelength (m)
03 Uses and dangers
Each type of EM wave is useful because of its specific wavelength and energy, but higher-energy waves also carry more risk:
- Ultraviolet: can damage skin cells, causing sunburn and increasing skin cancer risk
- X-rays and gamma rays: can damage or kill living cells, so exposure must be carefully controlled in hospitals
V Key vocabulary
| Term | Meaning |
|---|---|
| Electromagnetic spectrum | The full range of EM waves, ordered by wavelength and frequency. |
| Wavelength | The distance between two identical points on a wave. |
| Ionising radiation | High-energy EM radiation (like X-rays and gamma rays) that can damage living cells. |
| Vacuum | A space containing no matter, through which EM waves can still travel. |
? Quick check
Try to answer before you tap. Answers are hidden underneath.
Put these in order of increasing frequency: infrared, X-rays, radio waves, visible light.
Radio waves → infrared → visible light → X-rays.
Why are X-rays more dangerous to living cells than radio waves?
X-rays have a much higher frequency and carry more energy, which allows them to damage or kill living cells. Radio waves have very low energy and are generally harmless.
All electromagnetic waves travel at the same speed in a vacuum. If wavelength increases, what happens to frequency?
Frequency decreases (wave speed = frequency × wavelength is constant, so they are inversely related).