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Doppler Effect

Physics: Cambridge International A Level, topic 7.2.7

The Doppler Effect

The Doppler effect describes the phenomenon of the observed wavelength and frequency of waves changing when the source of the waves is moving with respect to an observer.

Types of waves

Types of waves

  • The Doppler effect can be experienced with all types of waves.
  • The wavelength and frequency of the waves do not actually change.
Approaching vs receding sources

Approaching vs receding sources

  • When the source of the waves is approaching, the frequency shifts upwards for observers.
  • When the source of the waves is receding, the frequency shifts downwards for observers.
Doppler equation

Doppler equation

  • The observed frequency fof_o is given by the equation:
  • fo=vv±vsff_o=\frac{v}{v\pm v_s}f
  • Where fsf_s is the frequency at the source, vv is the speed of the wave and vsv_s is the speed of the source.
  • The minus sign is used for motion toward the observer and the plus sign for motion away from the observer, producing the appropriate shifts up and down in frequency.

Test yourself on Doppler Effect

  • Which types of waves can be affected by the Doppler effect?

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