Doppler Effect Liu Po Shan Memorial College



Yüklə 445 b.
tarix05.02.2018
ölçüsü445 b.
#25111


Doppler Effect


Warm-up Activity

  • Watch the movie . . .

  • What is Doppler Effect ?



Summary .. 1

  • The Doppler effect is . . .

  • the apparent change in the frequency

  • of a wave motion

  • when there is relative motion

  • between the source and the observer.



Moving Source

  • Watch the Flash Animation . . .

  • What is the effect when the source is moving ?



Moving Source



Follow-up Activity

  • Watch the movie again . . .

  • Explain why the pitch of the whistle changes as the car passes the observer ?



Explanation to movie



Stationary Source



Moving Source - Change in 



Source Moving Toward Observer



Source Moving Away From Observer



Moving Source

  • Watch the JAVA animation . . .

  • What is the change in wavelength when the speed of the moving source changes ?



Summary ... 2A

  • The wavelength changes when the source moves.

  • The wave speed is independent of the speed of source.



Apparent Frequency – Moving Source

  • Watch the FLASH animation . . .

  • Notice the different frequency observed by stationary observers.



Change in Observed Frequency



Summary ... 2B

  • The apparent frequency observed by the observer changes.

  • For the source moving TOWARD the observer,

    • The wavelength reduces.
    • The apparent frequency increases.
  • For the source moving AWAY the observer,

    • The wavelength increases.
    • The apparent frequency decreases.


Moving Observer



Apparent Frequency – Moving Observer

  • Compared with the stationary observer:

    • Observer moving toward the source encounter more waves in each second. So the observer observes higher frequency. Apparent frequency increases.
    • Similarly, observer moving away from the source encounter less waves in each second. Therefore the apparent frequency decreases.


Apparent Frequency (moving Observer) – Relative Velocity

  • For moving observer,

  • the apparent frequency results from the change in relative velocity of the sound to the observer.

  • the wavelength does not change with the motion of the observer.



Moving Observers



Change in Observed Frequency



Summary ... 3

  • The apparent change in frequency f is known as the Doppler Shift.

  • The Doppler shift increases as the relative velocity between the source and the observer increases.

  • The Doppler effect applies to all forms of waves.



Moving Observer and Moving Source

  • Moving Source

    •  change in   f
  • Moving Observer

  •  change in relative velocity  f

  • Moving Source and Observer

  •  change in  and relative velocity  f



Equations – Moving Source and Observer







Yüklə 445 b.

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