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Questions tagged [doppler-effect]

The Doppler effect refers to change in the observed frequency of a wave if the observer and source are in relative motion.

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Relativity of simultaneity in train experiment-doesn't Doppler effect reveal simultaneity?

In Einstein's simultaneity thought experiment with the "moving" train and lightning strikes, wouldn't the observer on the train be able to deduce the simultaneity of the lighting strikes from the fact ...
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Which one is moving? [duplicate]

If there are two objects moving relative to each other at a constant velocity, is there any experiment the bodies themselves can do to determine which one is moving? EDIT: The comments say "NO". So ...
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How does a laser Doppler vibrometer work?

I know almost nothing about optics or lasers, but I understand mathematics. I'm trying to understand the basic principle behind a laser Doppler vibrometer, but I don't really get it. The main thing I ...
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What is the meaning of the formula $f_D = \frac{2v}\lambda$ in the context of the Doppler effect?

I'm reading the French Wikipedia article on laser vibrometers. With no real context, the article states that if a wave reflects off of a vibrating object, the value of the "frequency shift" is: $$f_D ...
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Doppler Effect and Speed relativity [closed]

I calculated that the frequency of the sound that reaches a recipient achieved when the recipient remains stationary and the source is towards him (vS = 34m / s) is not equal to the frequency of the ...
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How scientists know that the Redshift is because of moving objects and not due to local phenomena

I'm from engineering background and not firmly familiar with cosmological equations and concepts. but i know what Redshift is and how it is related to the Doppler effect. My question is how ...
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Doppler Effect and Energy variation

In the Doppler effect, we see that the frequency of sound that the observer hears changes according to the motion of the observer and source. For example, if the source is moving towards the observer, ...
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Does time really slow down in relativity, or is it an illusion caused by the Doppler shifting of light? [duplicate]

Does time really dilate, or is it only how we perceive time, which is in the form of light waves. When an object moves away from another object at very high speeds, the light takes longer to reach it ...
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Why is the derivation of the Doppler effect different for electromagnetic waves and mechanical waves?

I have read that the Doppler effect occurs for both mechanical and electromagnetic waves, the reason being that mechanical waves require a medium while electromagnetic waves don't. The formula for ...
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How does the relativistic Doppler effect model change if I want to include general relativistic effects also?

Derivations for the relativistic Doppler effect abound, which extends the description of the Doppler effect to include the effects of relativity in cases where the source or observer is moving at ...
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Proof for photon energy loss due to cosmological redshift

According to Doppler redshift, the frequency of the EM radiation decreases if the emitting object is receding from the observer - this produces the problem in the quantisation of energy - the observed ...
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How do you calculate the recession velocity?

$$ \begin{alignat}{7} && \frac{\Delta \lambda}{\lambda} & = \frac{v}{c} \\[2.5px] &\therefore & v & \approx \frac{\Delta \lambda}{\lambda}c \end{alignat} $$ If you want to find ...
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How does emitting light while moving not break the law of conservation of energy?

Say you have 2 identical LED monochromatic flashlights. The battery lasts exactly 1 hour. We are able to calculate the energy emitted as photons from the LED by Planck's Law: $E = h\nu$. Now if we ...
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Redshift - How can Z be greater than 1?

I'm having trouble understanding the equation for redshift: z = Δλ/λ ≈ Δf/f ≈ v/c If z = v/c and c = speed of light, how can z>1 (as nothing can exceed the speed of light)?
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How does conservation of energy explain the Doppler effect?

  According to modern physics (although I don't know exactly what the theories that back it up are,) the energy of a system is conserved within a frame of reference, such as in the example ...
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Do high speed particles see light as a different part of the EM spectrum due to the Doppler effect?

If a particle was travelling fast enough and had visible light shot at it, would the partice experience the light as if it was higher or lower wavelength? If so, would the particle see the incident ...
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How is it possible to have red shift along one axis and blue shift on another in a spiral galaxy arm?

I don't understand this image: If the stars are moving in roughly circular orbits why would red shift occur in the direction of the orbit and how would it be possible to have blue shift in two ...
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Doppler shift of light in uniform circular motion of source

Suppose, a monochromatic light source is undergoing uniform circular motion, and the observer is at the center of the circle. When the velocity of the source is perpendicular to the line joining the ...
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Doppler effect in accelerated motion [duplicate]

We know the formula for apparent frequency when source or observer or both are moving with uniform velocity. But what is the apparent frequency when they are accelerating with respect to each other.
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Does the gravitational Doppler effect affect charge?

I know that the charge of objects large enough to have distinct gravity is for the most part irrelevant, but large bodies do have (at a given instant) a fixed charge, which, granted, might be hard to ...
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How do astronomers know what wavelength the body will emit when it is at rest? [duplicate]

In the book of The First Three Minutes by Weinberg, at page 21, he talks about how do astronomers measure the speed of a luminous body along the line of sight by Doppler affect, i.e. the fractional ...
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Gravitational time dilation - Kip Thorne example

Please find in the images an example from Kip Thorne’s book ‘black holes & time warps’ on Gravitational Time Dilation. I do not understand the last sentences where the doppler effect results in ...
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The Doppler effect from a uniformly moving mirror

Regarding this paper by Aleksandar Gjurchinovski, The Doppler effect from a uniformly moving mirror on page 4 he says that eq. (8) can be transformed into eq. (12) by the use of "some simple algebra"...
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Is length contraction in Special Relativity the same as the Doppler Effect?

In my further reading of Special Relativity, the idea of length contraction when travelling at the speed of light is such that the length gets "squished" in the direction of travel. This immediately ...
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What does it mean by universe is expanding? I know that the universe is expanding because spacetime is expanding but again what does it mean?

I am aware about the balloon expanding analogue, where the galaxies are stuck on the balloon surface and here the balloon is our space time and as the balloon expand our galaxies also go apart. But ...
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What is this connection between clocks and the Doppler effect?

I derived an equation for the relativistic Doppler effect in the course of a routine problem: the frequency change of a photon moving in the $x$ direction, when considered a frame S' which has a ...
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Does Doppler Effect work this way?

If i am looking at an object which is moving towards me fast enough while i am at rest, then i would see the object's color shift towards blue in the Electromagnetic spectrum. But would the same ...
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A joke on the Doppler effect: does this make sense? [closed]

I'm currently writing something that explores the phenomenon of inside jokes, in which I use an astrophysicist joke that is meant to be undecipherable to the average reader. It was recommended to me ...
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Relativistic Doppler effect and Quantum Mechanics

Consider the situation below. I’m at a point in space along with a bunch of detector away from any gravitational field. I see a star moving away from me at a relative speed of $$v$$by measuring the ...
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how to work out conservation of energy and doppler shifts?

Let's modify a bit this question so that we use a single reference frame Let's imagine a laser shining light on an object. Let's put the reference frame at the object. In one instance the laser ...
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Mass changes by absorbing light energy with Doppler shift

Suppose you have a mass that is moving at relativistic speed wrt (with respect to) a powerful laser pointed at the mass. As the laser shines on the mass, assume it absorbs all the energy (and momentum)...
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Doppler effect for moving receiver and moving transmitter

For the case that receiver and transmitter are moving, the shift in frequency is given with $$f_{receiver} = f_{transmitter} \frac{c + v_{receiver}}{c - v_{transmitter}}$$ if they approach each ...
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Can the Doppler effect account for the increase in an object's energy with velocity?

I am aware that the relativistic mass can be expressed in terms of rest mass and momentum, which seems to be the canonical explanation, but I am looking at an alternative way of visualising the ...
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Moving sound sources and wavelength

How does a moving sound source physically compress the waves emitted in front of it and lengthen the waves emitted behind it? Virtually all descriptions of the doppler effect provide nice visuals of ...
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Doppler effect and shift in visible region and constant velocity of waves

I have learned that due to doppler effect the wavelength of light increases when source is moving away from observer. Also this proves big bang theory and also universe is expanding. Like red shift , ...
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A doubt on Doppler effect [duplicate]

As I learnt freq. observed by a observer from a moving source is given by $$f=f_0(1+v_s/v)^{-1}$$ If $$v_s=-v$$ f is infinity.Whats going on? Will Doppler effect will be observed if the source say is ...
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Doppler effect and constant velocity of a wave

Why doesn't the velocity of a photon change when it is emitted from a source moving with certain velocity? If a photon is a particle then it should have a lower velocity than one which is emitted from ...
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Laser / doppler cooling setup

Would it be practical to use doppler / laser cooling to cool a small surface (metal conductor) of 10 x 10 cm from 30 C to 20 C? Let's say using a setup like below? Where can I learn more about the ...
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Twin paradox Doppler shift explanation

I was reading the wikipedia article on the twin paradox and came upon the section describing it in terms of the relativistic Doppler shift (link). The image below illustrates the received signals ...
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Doppler Effect and Relativity

The equation for the Doppler effect is given by $$f_L = \frac{v+v_L}{v+v_S}f_S$$ where the velocities of both the source and the listener matter. My question is, how does this fit into Galilean ...
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Deriving relativistic Doppler shift for sound in without LT

This question is specifically about not using the Lorentz transformation but changing into the frame of reference of the wave by the relativistic velocity addition law. The situation is the following. ...
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109 views

What is the difference between these formulas? (Doppler effect)

The first formula I found in a video from Khan Academy: $$ f_0 = f_s\times \frac{v}{v\pm v_s} $$ $f_0$: Observed frequency (Hz) $f_s$: Source frequency (Hz) $v$: Wave velocity (m s$^{-1}...
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Doppler effect of sound waves in blood

When the sound waves that are produced by a ultrasound machine reflect there happens an increase into the frequency of the sounds. Why is that so? I think it should be the other way around because the ...
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How did ancient people describe the Doppler effect? [closed]

I've noticed the Doppler effect in the change of pitch of music as I ride past on my bicycle, so I assume in the old days people did this on horses too. Are there any ancient mentions or theories ...
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Quick check: relativity, rockets, clocks and the equivalence principle

One common thought experiment that introduces relativity on gravitational fields is the "clocks on an accelerating rocket": Paraphrasing Mr. Feynman: Suppose a rocket, with two clocks, one on each ...
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141 views

Are there experiments that measure relativistic Doppler effect?

Relativistic Doppler effect should be different from regular Doppler effect since there is also time dilation. Are there any experiments that prove that ?
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159 views

Why is light subject to the doppler effect?

Unlike sound propagating as motion of another substance, my understanding is that photons carry the electromagnetic energy themselves. And if I'm not mistaken, each individual photon "has" a specific ...
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Doppler effect and different frames

The equation of a travelling sine wave is given by $$y=Asin(wt-kx)$$ On seeing this from a different reference frame,we use galilean transformation,where,in new frame,replacing x by x-vt,the new ...
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Doppler shift and flux [closed]

I am trying to solve this problem: A body emits photons of frequency $\omega^*$ at equal rates in all direction in its rest frame. An observer is moving with speed V relative to the body in the x ...
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Relativistic Doppler Effect Rest Time vs Time Dilation Proper Time

For time dilation, both observers see the other as experiencing a time dilation symmetrically based on relative velocity to each other. In the twin paradox, however, one must be careful of which twin ...