Doppler Effect
Watch the movie . . . What is Doppler Effect ?
Summary .. 1 The Doppler effect is . . . 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
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. - The wavelength reduces.
- The apparent frequency increases.
For the source moving AWAY the observer, - The wavelength increases.
- The apparent frequency decreases.
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.
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 Moving Observer change in relative velocity f Moving Source and Observer change in and relative velocity f
Equations – Moving Source and Observer
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