Define the Doppler effect .

The Doppler effect (or Doppler shift) is the change in observed frequency caused by the relative motion between a source of sound (or light) and an observer.

What happens to the frequency of sound heard by a stationary observer when the source moves towards them?

The wavelength is shortened , so the observed frequency is higher (the pitch sounds higher).

What happens to the frequency of sound heard by a stationary observer when the source moves away from them?

The wavelength is lengthened , so the observed frequency is lower (the pitch sounds lower).

True or False? When a sound source is moving, the source and a stationary observer always measure the same frequency for the wave.

False. When the source is moving, the source and the observer disagree on the frequency of the wave — this disagreement is the Doppler shift.

A LevelPhysicsCambridge (CIE)Flashcards7. WavesDoppler Effect for Sound Waves

Doppler Effect for Sound Waves (Cambridge (CIE) A Level Physics): Flashcards

Exam code: 9702

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FrontDoppler Effect for Sound Waves
Define the Doppler effect.

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Cards in this collection (6)

Define the Doppler effect.
The Doppler effect (or Doppler shift) is the change in observed frequency caused by the relative motion between a source of sound (or light) and an observer.
What happens to the frequency of sound heard by a stationary observer when the source moves towards them?
The wavelength is shortened, so the observed frequency is higher (the pitch sounds higher).
What happens to the frequency of sound heard by a stationary observer when the source moves away from them?
The wavelength is lengthened, so the observed frequency is lower (the pitch sounds lower).
True or False?
When a sound source is moving, the source and a stationary observer always measure the same frequency for the wave.
False.
When the source is moving, the source and the observer disagree on the frequency of the wave — this disagreement is the Doppler shift.
In the Doppler shift equation $f_{o} = f_{s} (\frac{v}{v \pm v_{s}})$ , the denominator is v − v_s when the source is moving .......... the observer.
In the Doppler shift equation $f_{o} = f_{s} (\frac{v}{v \pm v_{s}})$ , the denominator is v − v_s when the source is moving towards the observer.
A source emits sound at 500 Hz and moves towards a stationary observer at 20 m s^-1. The speed of sound is 340 m s^-1. Calculate the frequency heard by the observer.
$f_{o} = f_{s} (\frac{v}{v - v_{s}}) = 500 \times (\frac{340}{340 - 20}) = 531 Hz$

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