Using the formula for the Doppler Effect, making sure all values are in their standard unit: The ambulance is approaching the observer.Therefore we use the form of the equation with the ‘minus’:
Demonstration of the Doppler Effect Apparatus Buzzer, string
Procedure Connect the buzzer to the string and turn it on. Have an observer stand a few metres in front of the demonstrator. Place buzzer on table and observe the pitch of note. Have the demonstrator swing the buzzer in a vertical circle and again observe the pitch of the rotating buzzer, as illustrated in Fig 10.19.
Observation A varying pitch can be heard.
Conclusion The apparent frequency of the note increases as the buzzer moves towards the observer and drops as it moves away.
SCIENCE,TECHNOLOGY & SOCIETY
Red shift All stars produce a characteristic ‘line spectrum’ based on the elements that make up that star4. Each line is an exact colour, based on a specific frequency. When a star (the source) is moving away from us (the observer), the apparent frequency is less than the actual frequency. For light, the lowest frequency of electromagnetic wave within the viable range is red. It is for this reason that when the apparent frequency is less than the real, each colour is shifted towards the red end of the spectrum, hence the term ‘red shift’.
4Line spectrum will be explained in Chapter 22. WAVES 165
