Aims of this Episode:

  • Compare and contrast Longitudinal and Transverse waves,
  • Describe uses of the different parts of the EM Spectrum,
  • Explain the Doppler Effect,
  • Explain Redshift as one example of The Doppler Effect.

What is the EM Spectrum?

Light. But not just visible light.

EM stands for ‘Electro-Magnetic’; the EM Spectrum is a type of wave formed by electric and magnetic fields. The wave ranges from very long (10 km between one wave and the next) to very short (less than the width of a hair between two waves) and everything in between.

As you move along the spectrum the properties of the wave change, so it is useful for different things. The wavelength and frequency are constantly changing along the wave. Scientists have broken the spectrum down into different ‘chunks’ based on their wavelength and frequency. At GCSE you need to know the details of each ‘chunk’. Click here for all the info.

The Doppler Effect

Waves are affected by movement (either of the source or the receiver).

If the source is moving towards you (or you are moving towards the source) the wave squashes up and the wavelength gets shorter.

If the source is moving away from you (or you are moving away from the source) the wave stretches out and the wavelength gets longer.

With sound this is heard as a change in pitch. With light, the entire spectrum shifts either to the blue end or the red end. When observing distant stars it was seen that the entire spectrum of each star had shifted towards the red end of the spectrum (longer wavelength) – this meant that the stars were moving away from us and hence, provided evidence for the theory of the Big Bang.

Click here for a great video explaining The Doppler Effect.

Also, click here for some more information about Longitudinal and Transverse waves.

S@S 022: The EM Spectrum (GCSE Physics)
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