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