The electromagnetic spectrum
| English | Chinese | Pinyin |
|---|---|---|
| electromagnetic spectrum | 电磁波谱 | diàn cí bō pǔ |
| radio waves | 无线电波 | wú xiàn diàn bō |
| microwaves | 微波 | wēi bō |
| infrared | 红外线 | hóng wài xiàn |
| ultraviolet | 紫外线 | zǐ wài xiàn |
| X-rays | X射线 | X shè xiàn |
| gamma rays | 伽马射线 | gā mǎ shè xiàn |
One family of waves
- Radio, the warmth of a heater, the light you see, the X-ray at a hospital — all the same kind of wave.
- Together they make the electromagnetic spectrum 电磁波谱.
- They all travel at the same high speed in a vacuum: $3.0 \times 10^8\ \text{m/s}$.
The order of the spectrum
- From longest wavelength to shortest: radio waves 无线电波, microwaves 微波, infrared 红外线, visible light, ultraviolet 紫外线, X-rays X射线, gamma rays 伽马射线.
- As you go that way: the wavelength falls, the frequency rises, and the energy rises.
- Visible light is just a thin slice in the middle.
The electromagnetic spectrum
Slide across the spectrum
Radio waves, visible light and gamma rays are all the same wave — only the wavelength changes, and with it the frequency, photon energy and everyday use.
In a vacuum, how do the speeds of radio waves, light and gamma rays compare?
All electromagnetic waves travel at the same speed in a vacuum, $3.0 \times 10^8\ \text{m/s}$.
Put these EM waves in order of wavelength, longest first.
Radio waves have the longest wavelength and gamma rays the shortest: radio, microwave, infrared, visible, UV, X-ray, gamma.
Going from radio waves toward gamma rays, the frequency:
As wavelength falls (radio → gamma), the frequency and the energy both rise.
What each one is used for
- Radio waves — radio and TV broadcasts.
- Microwaves — mobile phones, satellite TV, cooking.
- Infrared — remote controls, thermal imaging, grills.
- Visible light — seeing and photography.
- Ultraviolet — sterilising water, checking banknotes.
- X-rays — medical and security scans.
- Gamma rays — sterilising equipment, treating cancer.
A glass prism splits white light into the colours of the spectrum
Match each wave to a common use.
Microwaves carry phone signals, infrared works remote controls, and X-rays image bones.
The dangers
- The shorter, higher-energy waves are the dangerous ones.
- Microwaves — heat the water in body cells.
- Infrared — skin burns.
- Ultraviolet — skin cancer and eye damage.
- X-rays and gamma rays — damage cells and cause mutations.
Too much of which wave causes sunburn and skin cancer?
Ultraviolet has enough energy to damage skin cells, causing sunburn and skin cancer.
You've got it
- all EM waves travel at $3.0 \times 10^8\ \text{m/s}$ in a vacuum
- order (long → short wavelength): radio · micro · infrared · visible · UV · X-ray · gamma
- going that way: frequency and energy rise, wavelength falls
- higher energy → more dangerous (UV cancer, X/gamma cell damage)