I Classical waves and the Doppler shift

AI Thread Summary
The discussion centers on the Doppler effect and its relationship to wavelength and frequency as perceived by moving observers and stationary sources. A moving observer experiences a change in frequency due to the increased rate of wave crests passing them, but they may not perceive a change in wavelength. Conversely, when the sound source moves, both frequency and wavelength shift, creating the Doppler effect. The conversation also touches on the importance of understanding the reference frame of the observer and the medium in which the waves propagate. Ultimately, the Doppler shift is explained primarily through changes in frequency rather than wavelength from the observer's perspective.
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In the video:

The professor mentions how the wavelength will be the same for a moving observer vs a moving observer for a classical wave like a sound wave. However, how does that explain doppler shift? Don't we observe the effect because a moving observer measures a different wavelength than a stationary observer?
 
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Phys12 said:
However, how does that explain doppler shift? Don't we observe the effect because a moving observer measures a different wavelength than a stationary observer?
Think carefully about what the moving observer thinks, he does not necessarily think the wavelength has changed. Or read below:
When a sound source moves relative to the medium, then there is a Doppler-shift of the frequency and a Doppler-shift of the wavelength.

When an observer moves relative to the medium, then there is a Doppler-shift of frequency but no Doppler-shift of wavelength, according to the observer. (Wave-train is moving past me extra fast, that is why extra many wave-crests are passing me each second, says the observer)

(If anyone were to look inside the ear of an observer that is moving towards a sound source, he would find there a wave with a 'shortened' wavelength. But that is not the subject now, right?)
 
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jartsa said:
(If anyone were to look inside the ear of an observer that is moving towards a sound source, he would find there a wave with a 'shortened' wavelength. But that is not the subject now, right?)
I don't get this. Why will it be a different wavelength?
 
Phys12 said:
I don't get this. Why will it be a different wavelength?
Motion of the observer changes the pitch that the ear hears. No wind is blowing inside the ear, so the medium is at rest, in the rest frame of the ear.

Hmm maybe it would be better to consider a car that is driving towards a sound source, and the sound waves in the air inside the car.
 
Phys12 said:
However, how does that explain doppler shift? Don't we observe the effect because a moving observer measures a different wavelength than a stationary observer?
Did you look at the Doppler formulas? Does wavelength appear in them?
 
A.T. said:
Did you look at the Doppler formulas? Does wavelength appear in them?
Not that I remember. So, Doppler shift happens for normal waves (non-quantum) because of change in frequency because of a moving observer or because of change in wavelength and frequency because of the moving source. Is that correct?
 
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