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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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What is the relationship between relativity and the Doppler effect?

My sister just watched this video about space contraction (Spanish), and asked me if this is related to doppler effect. In the clip they also introduce the idea that a bat would be affected by ...
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Is this derivation of the Doppler effect for sound waves valid?

I was recently considering how to justify the formula relating to the Doppler effect for sound waves to a group of eleventh grade students who are likely encountering it for the first time. The ...
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Question about twin paradox

I just started to learned modern physic for a two weeks, and the i got some problem to understand about the resolution of twin paradox I have attached two pages of picture above that makes me ...
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25 views

Dopplar Effect with Relative Velocities

My understanding of the classical Doppler effect formula was that the velocities (of the receiver and source) would be relative to the medium in the following formula: However, Wikipedia has an ...
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1answer
55 views

Deriving Doppler effect in observer's frame

I am attempting to find the Doppler factor from the frame of the observer. In the frame of the observer, the source is moving at velocity $v$ towards the observer. Since the source emits at time ...
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1answer
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Doppler effect when two bodies are not moving in straight line [closed]

What is a Doppler line? Why are the velocity components taken along Doppler line as shown here? And what is the derivation of formula $$f_0=f \frac{v+v_1 \cos\theta_1}{v-v_2 \cos\theta_2}$$ where $...
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61 views

Apparent frequency as function of distance

So the Doppler effect says that the frequency of sound changes due to relative motion of source and observer. My question is if there any expression that tells how the apparent frequency changes in ...
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12 views

Doppler shift in Acousto-Optic modulators

The interaction between a beam of light and an acoustic wave is commonly modelized as a photon-phonon scattering phenomenon. Applying the conservation of energy we have that $$ \hbar\nu_1=\hbar\nu_0\...
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1answer
41 views

Doppler effect and frame of reference

We know that in an inertial frame we can never tell if the frame is really at rest or moving with constant velocity but can’t we check if there is a change in frequency by a sound emitted by the frame ...
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1answer
37 views

Can Doppler effect produce effect beyond visible region

Can Doppler effect produce changes beyond visible region ? Like suppose a star that is moving towards us emitting a violet color but due to Doppler effect we are receiving wavelengths lying in region ...
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Reflective photon rocket

A space-craft, also of rest-mass $M_0$ and initially at rest, is propelled by reflecting a plane-parallel beam of photons, generated at a rate $αM_0$ from a stationary source mounted on the launch pad,...
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Is the period a physical observable in General Relativity?

I am currently seeing the classical tests of GR. To justify the introduction of a test based on the Doppler effect, the professor says that the previous test ( Shapiro and echo-radar test ) is based ...
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Lack of invariance of relativistic doppler effect for inertial frames?

The equation for the relativistic doppler effect in a medium where waves travel at speed $c_m$ is $$\frac{f_r}{f_s} = \frac{c_m - v_r}{c_m-v_s}\frac{\gamma_r}{\gamma_s}$$ My question is whether this ...
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1answer
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If 2 spaceships approaches each other at 0.99c, how much blue shift would they see? [closed]

Imagine these 2 spaceships moving at 0.99c toward each other and speed isn't additive how much blue shift would they see? I know how to calculate when the scenario is spaceship vs Earth but how about ...
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1answer
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Lorentz transformation of intensity

I have come up with an expression for the way intensity transforms, however it is different to the book, and I cannot seee where I have gone wrong. So we both start the same way: $$ \frac{I}{I_0}=\...
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1answer
36 views

Relativistic Doppler Effect - calculate frequency $f'$ and $f$ in references $S'$ and $S$

Considering that $S$ (fixed) and $S'$ are inertial references which coincides when $t=t'=0$ and their coordinates $(ct,x,y,z)$ and $(ct',x',y',z')$ are related by Lorentz's transformations, calculate ...
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Derivation of formulas in Doppler‘s effect in light [duplicate]

I was wondering how was the formula for Doppler effect in light i.e. $f=\sqrt{\frac{(1-v/c)}{(1+v/c)}}f$ was derived. I understood how it is derived for sound but I am unable to understand how it is ...
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A question about horizontal doppler effect on galaxy hydrogen radiation observation

The figure shows the positions of the solar and neutral hydrogen regions A to D rotating in a circular orbit relative to the center of the galaxy. The sun and A to D assume a Kepler rotation. ...
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1answer
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Doppler shift equivalent for a short nonsinusoidal pulse

All of my search results explain Doppler shift in the frequency domain. None explain what happens for a moving source or observer when the transmission is a short unmodulated 'time domain' pulse. I ...
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2answers
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Understanding The Solution To A Doppler Effect Problem [closed]

Can someone help me understand the solution to this problem? What I don't understand is 2 things: How has the radiation been Doppler shifted twice? I don't get what about the scenario leads to this ...
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1answer
41 views

Doppler effect contradiction when counting wave fronts

For concreteness, let's take a source moving away from a stationary observer. The observed frequency will be less than the emitted frequency, so for any given time interval, the observer will count ...
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0answers
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Relativistic photoelectric effect

Suppose, one conducted an experiment with a monochromatic light shining on a metal plate with a certain work function. It turns out the electron is ejected. When this experiment is observed by another ...
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1answer
59 views

Doppler effect in light (Observer moving away from source)

I understand this intuitively and can picture it in my head, but when I do it on paper, the result is a sign difference that I cannot understand According to this diagram the wavelength = ct-vt = t(c-...
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1answer
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Acousto-optical modulator (AOM)

Suppose the RF frequency of the driver of an AOM is 40 MHz. I understand that it will Doppler shift the diffracted first order beam by 40 MHz but how does it modulate the amplitude of that first order ...
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3answers
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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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3answers
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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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1answer
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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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1answer
55 views

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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1answer
83 views

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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2answers
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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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4answers
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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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0answers
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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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2answers
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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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1answer
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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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3answers
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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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1answer
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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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2answers
146 views

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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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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3answers
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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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227 views

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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1answer
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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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1answer
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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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1answer
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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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2answers
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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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1answer
28 views

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 ...