Each waveband has useful properties
Definition
Electromagnetic spectrum
The continuous range of electromagnetic waves arranged according to wavelength or frequency.
- All electromagnetic waves travel at the same speed in a vacuum, but their wavelengths and frequencies make them interact differently with matter.
- A suitable use depends on transmission, absorption, diffraction, heating, ionisation and the information that the wave can carry.
Communication uses longer wavelengths
- Radio waves are used for broadcasting because they can travel long distances and some frequencies diffract around obstacles.
- Microwaves are used for satellites because they pass through the atmosphere, carry high data rates and can be directed in narrow beams.
- Microwaves heat water-rich food when their energy is absorbed.
- Infrared is used in remote controls, short-range links and thermal imaging because warm objects emit it.
- Visible light carries data through optical fibres and forms images for vision and photography.
Short wavelengths image and treat
- Ultraviolet is used in fluorescent lamps, security marking and sterilising surfaces because it causes fluorescence and can kill microorganisms.
- X-rays image bones because dense bone absorbs more X-rays than soft tissue, creating contrast at the detector.
- Gamma rays sterilise sealed medical equipment because they penetrate packaging and kill microorganisms.
- Focused gamma radiation is used in radiotherapy to damage cancer cells.
Example
Selecting radiation for a satellite link
The signal must pass through the atmosphere, carry information and form a narrow beam.
Microwaves satisfy these requirements, so dishes can transmit and receive the signal accurately.
Lower-frequency radio waves diffract more and require larger aerials, making them less suitable for this link.
Exam technique
Justify the use
Name a property of the radiation.
Link the property directly to the task.
Include the relevant hazard or control when ionising radiation is used.
Common Mistake
Do not say bones reflect X-rays; bones absorb more X-rays than soft tissue, creating contrast at the detector.
Self review
- Why are microwaves suitable for satellite communication?
- How does thermal imaging use infrared radiation?
- Why do X-ray images show bones clearly?
- Why can gamma rays sterilise sealed equipment?
