Summary and Main Ideas

Summary

• The Doppler effect is a change in observed frequency due to the relative motion of a source and an observer.

• The following equation can be used to calculate the frequency of the wave according to the observer or listener:

  \[{f}_{L}=\left(\frac{v+{v}_{L}}{v+{v}_{S}}\right){f}_{S}\]

• If the direction of the wave from the listener to the source is chosen as positive, the velocities have the following signs:

  Source moves towards listener	\({v}_{S}\): negative
  Source moves away from listener	\({v}_{S}\): positive
  Listener moves towards source	\({v}_{L}\): positive
  Listener moves away from source	\({v}_{L}\): negative

• The Doppler effect can be observed in all types of waves, including ultrasound, light and radiowaves (explored in another tutorial).

• Sonography makes use of ultrasound and the Doppler effect to determine the direction of blood flow.

Table: Units used in Doppler effect