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Electromagnetic (EM) Waves (Edexcel IGCSE Physics)
Revision Note
Properties of EM waves
- Light is part of a continuous electromagnetic spectrum that consists of the following types of radiation:
- radio
- microwave
- infrared
- visible
- ultraviolet
- x-ray
- gamma ray
- All waves in the electromagnetic spectrum share the following properties:
- They are all transverse
- They can all travel through free space (a vacuum)
- They all travel at the same speed in free space
The EM spectrum
- The types of radiation found in the electromagnetic spectrum have a specific order based on their wavelength (and frequency)
- This order listed above has:
- Radio waves at the top because they have the longest wavelength (and lowest frequency)
- Gamma rays at the bottom because they have the shortest wavelength (and highest frequency)
- Wavelength and frequency are inversely proportional to each other:
- An increase in wavelength is a decrease in frequency (towards the red end of the spectrum)
- A decrease in wavelength is an increase in frequency (towards the violet end of the spectrum)
- This is explained by the Wave equation
The types of radiation in the EM spectrum from longest to shortest wavelength
Visible light is just one small part of a much bigger spectrum: The electromagnetic spectrum
Visible Spectrum
- Visible light is the only part of the EM spectrum detectable by the human eye
- However, it is only a very small part of the whole electromagnetic spectrum
- In the natural world, many animals, such as birds, bees and certain fish, can perceive beyond visible light and use infra-red and UV wavelengths of light to see
- Each colour within the visible light spectrum corresponds to a narrow band of wavelength and frequency
- The different colours of waves correspond to different wavelengths:
- Red has the longest wavelength (and the lowest frequency)
- Violet has the shortest wavelength (and the highest frequency)
The colours of the visible spectrum
The colours of the visible spectrum: red has the longest wavelength; violet has the shortest
Examiner Tip
See if you can make up a mnemonic to help you remember the order of the colours of visible light in the EM spectrum!.
One possibility is:
Raging Martians Invaded Venus Using X-ray Guns
To remember the colours of the visible spectrum you could remember either:
- The name “Roy G. Biv”
- Or the saying “Richard Of York Gave Battle In Vain”
You could even combine both to have a mega mnemonic:
Raging Martians Invaded Roy G. Biv Using X-ray Guns!
The electromagnetic spectrum is usually given in order of decreasing wavelength and increasing frequency i.e. from radio waves to gamma waves
Remember:
- Radios are big (long wavelength)
- Gamma rays are emitted from atoms which are very small (short wavelength)
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