THE DOPPLER EFFECT
Section 9.5
Key Terms
Doppler Effect
Doppler Effect
As an emergency vehicle approaches, the pitch (frequency) of the siren changes. As the siren approaches you, the waves are
compressed and the sound entering your ear is of a higher frequency than the sound generated by the siren.
As the siren moves away from you, the opposite occurs and the sound entering your ear is of lower frequency than the sound generated by the siren
Doppler Effect
For Example…
Sheldon’s Take
Doppler Effect Cont’d
Not all moving sources of sound will generate a Doppler effect. Speed of moving source must be a
reasonable fraction of the speed of sound. Emergency vehicle moves ~ 30 m/s Speed of sound ~ 332 m/s
Therefore Vehicle moves at ~ 10% speed of sound
Calculating the Doppler Effect
Where fobs = frequency of observer vsound = local speed of sound vdetector = speed of detector vsource = speed of source f0 = frequency of source
Summary
Homework
Page 435 Questions 1-7