Doppler Effect

[Saber]

Two  questions  about the  doppler effect..........

 

Does  it  also  apply  in reverse ??   i mean  a stationary    sound  source  & a   mobile   observer (  hearer )

 

And   .....does it  apply  to  other  forms  of  waves ?  like  electromagnetic  ones ?      or  light ???

 

Thanx .......

 

 

[mistermack]

As far as I know the answer is yes to all. It's known as the relativistic Doppler effect to give it it's full title. And light IS electromagnetic radiation, and you do get a red/blue shift effect because of Doppler, which is useful in cosmology telling us the relative motion of certain stars. 

https://en.wikipedia.org/wiki/Relativistic_Doppler_effect  

[exchemist]

1 hour ago, Saber said:

Two  questions  about the  doppler effect..........

 

Does  it  also  apply  in reverse ??   i mean  a stationary    sound  source  & a   mobile   observer (  hearer )

 

And   .....does it  apply  to  other  forms  of  waves ?  like  electromagnetic  ones ?      or  light ???

 

Thanx .......

 

 

It is an effect you get with any propagating wave. All that matters is relative motion between the source and the receiver. (It is in any case arbitrary which of the two you say is "stationary", since that depends on the frame of reference of the observer.)

The maths works a bit differently for light, since that travels at c, necessitating use of the relativistic Doppler effect. But the effect is qualitatively the same as with the classical Doppler effect, which one uses for sound waves for example.

 

[exchemist]

1 hour ago, exchemist said:

It is an effect you get with any propagating wave. All that matters is relative motion between the source and the receiver. (It is in any case arbitrary which of the two you say is "stationary", since that depends on the frame of reference of the observer.)

The maths works a bit differently for light, since that travels at c, necessitating use of the relativistic Doppler effect. But the effect is qualitatively the same as with the classical Doppler effect, which one uses for sound waves for example.

 

Addendum: I got this a bit wrong. What makes the relativistic version different is that the speed of light is independent of relative motion between source and receiver, whereas a classical wave moves at a fixed speed in the medium that transmits it. 

[Lorentz Jr]

6 hours ago, Saber said:

Does  it  also  apply  in reverse ??   i mean  a stationary    sound  source  & a   mobile   observer (  hearer )

Yes.

6 hours ago, Saber said:

And   .....does it  apply  to  other  forms  of  waves ?  like  electromagnetic  ones ?      or  light ???

Yes, except light is an electromagnetic wave.

Classical Doppler effect:

[math]\displaystyle \frac{f_o}{f_s} = \frac{c-v_o}{c+v_s}[/math]

where f is frequency, o is the observer, s is the source, c is the speed of the wave, and positive speeds v_s and v_o indicate motion of the source or observer (relative to the medium of the wave) away from the other object.

Relativistic Doppler effect:

[math]\displaystyle \frac{f_o}{f_s} = \sqrt{\frac{c-v}{c+v}}[/math]

where v is the relative speed between source and observer, and positive v means they're moving away from each other.

Edited February 3, 2023 by Lorentz Jr

[Janus]

Just an addition to the previous post. In the Classical Doppler shift equation, v_o and v_s refer to the velocity of the observer and source with respect to the medium through which the waves are propagating. 

As result, you get a different answer if you have the source moving with respect to the medium than if it is the observer moving with respect to the medium.

Whereas with the relativistic equation, there is no medium and the answer only depends on the relative velocity between source and observer.

Also, There is a typo in the equation given for Relativistic Doppler shift. It should be v-c for upper part of the fraction.

You will often see this equation written with 1-ß and 1+ß instead, where ß = v/c

[Genady]

I've never heard of a Doppler effect on gravitational waves. Is it the same old relativistic Doppler effect, or some modifications appear?

[Lorentz Jr]

Some cross-editing there. Using the same conventions in the two formulas shows their similarities and differences as clearly as possible.

[studiot]

52 minutes ago, Genady said:

I've never heard of a Doppler effect on gravitational waves. Is it the same old relativistic Doppler effect, or some modifications appear?

 

There are lots of Gwave detector types and some of the sources are known to be moving away at appreciable speeds so it is not suprising that LIGO offer this

 

Quote

https://www.ligo.org/science/Publication-VSR4PulsarNarrowband/

The motion of the gravitational wave detector around the Earth causes a frequency shift of the nearly sinusoidal received signal due to the Doppler effect and a time-depending amplitude variation as the orientation of the gravitational wave observatory with respect to the star changes.

 

Edited February 3, 2023 by studiot

[Genady]

1 hour ago, studiot said:

 

There are lots of Gwave detector types and some of the sources are known to be moving away at appreciable speeds so it is not suprising that LIGO offer this

 

 

Thank you. It only says that such effect exists, which is expected. Since nothing else is said by LIGO or by Wikipedia, I assume it is not different from the effect on EM wave (that was my question.)

Edited February 3, 2023 by Genady

[Markus Hanke]

9 hours ago, Genady said:

I assume it is not different from the effect on EM wave (that was my question.)

Yes, it’s indeed not different from EM waves. What is different though is the way gravitational waves interact with one another, and with any background curvature that might be present.