16 the doppler effect


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16 the doppler effect

  1. 1.  What have you observed with the sound of these vehicles as they pass by at a certain speed?  What explanation can offer to account for this observation?  What are the key variable involved?
  2. 2.  The apparent change in the frequency of a source of wave due to the motion of the source and/or the observer  Developed  The by Christian Doppler in 1842 difference of the true frequency and the apparent frequency is called the Doppler Shift
  3. 3. The following symbols will be used in the definitions: f is the true frequency  f’ is the apparent frequency v is the velocity of the sound (air)  vs is the velocity of the source  vo is the velocity of the observer λ is the true wavelength  λ’ is the apparent wavelength
  4. 4. f ’ = [ ( v ± vo ) / v ] f  ( + ) means the observer is moving towards the source  ( - ) means the observer is moving away from the source
  5. 5. f ’ = [ v / ( v ± vs ) ] f  ( + ) means the source is moving away from the observer  ( - ) means the source is moving towards the observer
  6. 6. f ’ = [ ( v ± vo ) / ( v ± vs ) ] f  NOTE: please refer to case 1 and case 2 and analyze the situation of the observer and the source respectively.
  7. 7.  When a wave source moves toward a receiver, does the receiver encounter an increase in wave frequency, wave speed ,or both?  Does the Doppler Effect occur for only some types of waves or all types of waves?
  8. 8.  named after Austrian physicist and philosopher Ernst Mach  Used to describe speed of objects that are travelling close to, or above the speed of sound.  The ratio of the speed of the object and the speed of sound in the medium. M = speed of object / speed of sound
  9. 9.  this is heard as a sonic boom when an airplane passes over; this is the result of the compilation of sound waves generated by a source that moves at equal or greater velocity than the sound it creates
  10. 10. 1. An ambulance traveling at 20. m/s sounds its siren at a frequency of 256Hz. What apparent frequency will you hear if the ambulance is: ( assume air temperature to be at 25°C ) a. approaching you? b. moving away from you? 2. A car traveling at 30. m/s sounds its horn as it overtakes and pass another car traveling at 20. m/s in the same direction. If the frequency of the horn is 500. Hz, what is the frequency heard by the driver in the slower car: a.) before b.) after the car has passed? Assume sound speed to be at 350. m/s.