What is Doppler: Definition and 747 Discussions

The Doppler effect or Doppler shift (or simply Doppler, when in context) is the change in frequency of a wave in relation to an observer who is moving relative to the wave source. It is named after the Austrian physicist Christian Doppler, who described the phenomenon in 1842.
A common example of Doppler shift is the change of pitch heard when a vehicle sounding a horn approaches and recedes from an observer. Compared to the emitted frequency, the received frequency is higher during the approach, identical at the instant of passing by, and lower during the recession.The reason for the Doppler effect is that when the source of the waves is moving towards the observer, each successive wave crest is emitted from a position closer to the observer than the crest of the previous wave. Therefore, each wave takes slightly less time to reach the observer than the previous wave. Hence, the time between the arrivals of successive wave crests at the observer is reduced, causing an increase in the frequency. While they are traveling, the distance between successive wave fronts is reduced, so the waves "bunch together". Conversely, if the source of waves is moving away from the observer, each wave is emitted from a position farther from the observer than the previous wave, so the arrival time between successive waves is increased, reducing the frequency. The distance between successive wave fronts is then increased, so the waves "spread out".
For waves that propagate in a medium, such as sound waves, the velocity of the observer and of the source are relative to the medium in which the waves are transmitted. The total Doppler effect may therefore result from motion of the source, motion of the observer, or motion of the medium. Each of these effects is analyzed separately. For waves which do not require a medium, such as electromagnetic waves or gravitational waves, only the relative difference in velocity between the observer and the source needs to be considered, giving rise to the relativistic Doppler effect.

View More On Wikipedia.org
Recent contents Top users
  1. J

    Calculating Speed with a Radar Gun: Exploring Doppler Shifts

    Radar Guns are used to measure the speed of a moving object. The wave it emits experiences two Doppler shifts. How does the radar gun then use the difference in frequency of the initial wave it emits and the frequency of the final wave it receives to calculate the speed of the object...
  2. PsychonautQQ

    What is the significance of relative velocity in the Doppler effect?

    Homework Statement http://grephysics.net/ans/8677/12 I don't understand how it increases it's frequency by a factor of 10, I mean the total velocity goes from 1 to 1.9, therefore It seems like it should increase from 1kHz to 1.9kHz. Why is my 'common sense' wrong?
  3. B

    Doppler Effect: Speed Relative to Ground, Source, or Listener?

    hi i just want to ask about the formula of Doppler Effect . The speeds of the listener VL and the source Vs are relative to the ground, source, or listener ?
  4. P

    Photons and the Doppler effect

    I am currently capturing and analyzing spectra. My analysis software includes allowances for Doppler shifts resulting from relative radial motion between source and observer, and also Earth’s rotation. Results are accurate . The basic introduction to the Doppler effect generally starts with...
  5. D

    Energy Change Due to Doppler Shift

    Hello all, so let's suppose a photon is being gravitationally red or blue shifted changing its frequency which ultimately changes its energy, where does this energy change come from?
  6. PsychonautQQ

    Problem with basic doppler effect question

    Homework Statement The source of a 1 kilohertz sound is getting closer to the listener at a speed of .9 times the speed of sound. What frequency does the listener hear? Homework Equations fl = ((v-vs) / (v + vl))fs The Attempt at a Solution ((343+343(.9)) / 343)*1000=1900 Hz...
  7. G

    Doppler shift with 2 trombones

    Homework Statement Mary is blowing her trombone at 400hz. Paul is approaching her at speed v, blowing the same type of trombone. These trombones has a maximum frequency of 500hz. What is the maximum speed Paul can approach Mary, and still cancel out her trombone noise? Homework...
  8. arnesinnema

    Doppler effects and relativity

    I’ve got a question. Say we have a medium traveling through a pipe at speed v. The soundspeed of the medium is vs. The speed of the wavefronts to an stationary are approximately v-vs and v+vs when both v and vs are much smaller than the lightspeed c. However what happens when v=c? Do the...
  9. Solarmew

    Is the Relativistic Doppler Shift Formula Correctly Applied in this Problem?

    I was just wondering if this problem is right and I'm missing something or ... http://www.astronomy.ohio-state.edu/~ryden/ast143/ps3_soln.pdf Cuz I'm reading the GRE book and it says here to use the relativistic Doppler shift formula. So the problem in the link would need to be solved like...
  10. M

    Laser Doppler Anemometry and CFD - 3rd Year Project

    Hi, I am just about to go into my 3rd year of my Mechanical Engineering Degree and have decided to do a project with the following description: "Laser Doppler Anemometry (LDA) is a non-intrusive technique used to measure flow velocities and turbulence quantities in a fluid flow. The...
  11. J

    System model of doppler shifted laser

    Hello all, I am trying to model a received laser signal, x(t), reflected off a moving target. I am currently trying to model for both frequency change due to Doppler shifting as well as a time-varying phase shift, θ(t), due to the continuous change in distance from the target. My current...
  12. P

    Moving Masses & Doppler Shifts in Flat Space-Time

    Lets imagine in idealized situation in which we have an obsever in flat space-time, surrounded by distant static objects, which have no doppler shift (as they aren't moving and there isn't any gravity). Now, we introduce a massive object with a relativistic flyby. We expect the distant...
  13. A

    Solving the Doppler Effect for Ambulance Moving in Expressway

    Homework Statement An ambulance is moving in an expressway at a speed of 60km/hr from East to West(from A to B) as shown in the figure with a siren of 880Hz. Let the frequecies of the siren sound detected by an observer located at point O be Va and Vb as the ambulance just passes point A and...
  14. T

    Doppler Effect Formula Question

    I am a high school teacher and I just came across this issue when I began teaching at a new school. I am positive that if I am stationary and a 500 Hz siren comes towards me at 30 m/s, then the observed frequency will increase. I am 99% positive that if the 500 Hz siren is stationary and I move...
  15. P

    Analysis of Doppler Effect - Seeking Validation/Criticism

    I have done a little analysis of Doppler Effect and have tried to compile my thought in a document. My background is not physics thus, I am seeking validation/criticism from this community. I would very much appreciate it if you went through my work and pointed out where I might be wrong. The...
  16. R

    Doppler Shift/ Doppler effect HELP

    Doppler Shift/ Doppler effect! HELP 1. A police car is traveling at a constant speed of 110. km/h with a radar gun which generates and detects radiowaves. The police car and the ambulance drive directly towards each other. The radar gun produces radiowaves with a wavelength of 0.0440 m. An...
  17. A

    Doppler Effect (Sound) - Source moving away from the Observer

    Hi! I was doing some exercises about the doppler effect on sound until I found this problem that I can't find the solution! "A source of sound of frequency f0 moves horizontally at constant speed u in the x direction at a distance h above the ground. An observer is situated on the ground at...
  18. B

    Doppler shift, c, observation, recession, spacetime expansion

    Hi all, It is my understanding that a Doppler shift is the result of a change in wave frequency due to a change in distance of a signal source, relative to the observer. I assume that the change in distance must be continuous, in order to observe a Doppler effect: frequency increase =...
  19. U

    Archived Planck's law and doppler effect

    Hello, We proved something during the course but I totally forgot how to do it.. Homework Statement Prove that Planck's Law E=h*u is deduced from the equation of Doppler effect u'=u*√((1-β)/(1+β)) Homework Equations Lorentz transformationThe Attempt at a Solution If we take a beam of light of...
  20. F

    Wave superposition and Doppler effect.

    Homework Statement A student is at some point between two sound reflecting walls. He's holding a tuning fork and runs towards one of the walls at 5m/s. The pulsating frequency he hears is 8Hz. ¿What's the sound frequency emitted by the tuning fork? Answer: 137.17 Hz. I know I'm supposed to use...
  21. S

    Doppler Effect Question regarding wavelength changing

    Homework Statement A listener L hears the siren from a moving police car ,S, which is moving away from the listener with a speed of v = 20.0 m/s. The listener is moving at 10.0 m/s towards the car. There is a wind blowing with a speed of v(wind)= 10.0 m/s from S to L. The siren is emitting...
  22. A

    High-Energy Doppler Shift & Pair Production

    Hi all, Let's say you are at rest with respect to the galaxy, and you have low energy photons all around you. Now, if I crank my energies up relatvisitcally, the frequency and thus E = hf of those photons will increase. Red Light becomes Blue Light, Blue Light becomes UV, UV to X-ray, and...
  23. T

    How Fast is the Motorcycle in This Doppler Effect Scenario?

    Homework Statement A hooter on a motorcycle sounds a note of 6000Hz when the motorcycle is stationary. You detect a shift in frequency of 30Hz when the motorcycle approaches you and then recedes from you. Calculate the speed of the motorcycle. Speed of sound = 340m/s Homework Equations...
  24. X

    Simple Harmonic motion and Doppler effect question

    Homework Statement So you're being pushed on a swing by someone who is whistling at a constant 60Hz. At the bottom, Vmax is 4 m/s. Explain what you hear as you swing toward and away from the source of whistling (speed of sound is 343 m/s for this problem). Homework Equations Observed...
  25. N

    Doppler Shift Special Relativity Question

    Homework Statement light signal of frequency 33 MHz is reflected off a (radio)mirror that is moving toward you at half the speed of light. What is the reflected frequency in Hz?Homework Equations f_f = f*sqrt((1-v/c)/(1+v/c)The Attempt at a Solution The mirror and light wave are approaching...
  26. L

    Electromagnetic waves, doppler effect

    I pay for chegg to help me with physics but sometimes I'm not quite sure if the site is right. Could you please tell me if I am doing the below problem correctly? My way is different than Chegg's so I would just like to make sure I am not wrong because I am getting different answer than that...
  27. A

    2D Doppler Shift / Relative Velocities

    Hi, I'm trying to adapt the doppler shift formula for a stationary listener and a source traveling in a straight line towards/away from the listener to the case where the source does not move straight towards the listener. For example, suppose that I am looking north and train further in the...
  28. Jalo

    Sound waves propagation and the doppler effect

    Homework Statement A lighthouse emits a noise with a frequency of 2000 Hz in the direction of the sea, with a power of 100W. Consider the speed of sound, vs, to be 341 m/s. A ship approaches the coast with a speed of 30 km/h and produces noise with an intensity of 40dB. Consider it is...
  29. G

    Conflicting Transverse Doppler Shift Equations?

    http://en.wikipedia.org/wiki/List_of_relativistic_equations#Doppler_shift and http://www.physics.umanitoba.ca/~souther/waves02/feb0402/sld011.htm If you look at the derivation on Wikipedia: v' = γv But the one on Uni of Manitoba shows: f' = f0(1-β^2)^(1/2) or f' = f/γ...
  30. Daaavde

    How precise can Doppler shift be measured in detecting exo-planets?

    As the title says, I'm interested in the precision a Doppler shift can be revealed. That's why I read that it's possible to detect exo-planets by measuring the Doppler shift of the star's spectra. Works like this: the stars moves, since it moves back and forth is spectrum suffer from Doppler...
  31. I

    Help with Doppler effect radar question.

    Can any of you help. I am trying to fight a speeding ticket with a written declaration. To be honest I feel it was so unfair I was going with the speed of traffic and marked me as going 6mph more. I am sending the court explaining how I believe this was wrong and a radar error. Taking Physics...
  32. B

    SR, Doppler effect on rotating disk

    Homework Statement taken directly from Rindler A large disc rotates at uniform angular velocity ω in inertial frame S. Two observers O1 and O2 ride on the disc at radial distances r1 and r2. They carry clocks C1 and C2 they adjust to keep with clocks time with S, i.e., they have been adjusted...
  33. W

    How does the Relativistic Doppler Effect Affect Observed Wavelengths?

    Homework Statement A light source moves away from an observer at a speed vs that is small compared to c. show that the fractional shift in the observed wavelength can be approximated by \frac{\Delta \lambda}{\lambda} \approx \frac{v_2 }{c} Homework Equations f' = \frac{\sqrt{1+ \frac{v}{c} }...
  34. M

    How do you finish rearranging the Doppler shift formula

    Homework Statement i am using the Doppler shift formula Fs=F0(1/1+-(vsource/c) i can rearrange it to an extent but when i use it to find my answer i i need to divide it by two in order to do it, every time. I would just like to understand why this is, or if i am doing it completely wrong...
  35. S

    Doppler Effect: Moving Objects & Wavelengths

    Hello, what is referred to that every moving body has an associate wavelength ? thank you
  36. A

    How would you solve this physics problem on relativity and the doppler effect?

    Homework Statement Police radar detects the speed of a car as follows: Microwaves of a precisely known frequency are broadcast toward the car. The moving car reflects the waves with a doppler shift. The reflected waves are received and combined with an attenuated version of the tansmitted wave...
  37. V

    Calculating Velocity and Direction Using the Doppler Effect

    Homework Statement An engineer at an underwater military station listens for submarines by sending an ultrasound sonar ping that has a frequency of 3.75 MHz. A second ping returns with a frequency of 3.80 MHz, indicating that the object is now moving. What is the object’s velocity? In...
  38. N

    Finding velocity of a vehicle using Doppler Shift for sound

    Homework Statement You are standing on the side of the Trans-Canada Highway as the Physicsmobile approaches you. As it approaches, you hear an engine noise of 1100 Hz. After it passes, you hear an engine noise of 950 Hz. How fast was the Physicsmobile travelling? Homework Equations...
  39. K

    How can doppler effect occur when c is indepedent of motion?

    I thought the speed of light was constant independent of the motions of the observer and light source. So I don't understand how the doppler (blue-red) shift can be observed on incomming or receding astronomical light sources? Speed also varies depending on the medium it travels through, so...
  40. P

    Unfortunate Doppler Discussion in Nice Paper

    In another thread, Dalespam posted this paper: http://arxiv.org/abs/gr-qc/0311038 The paper is, overall, very nice and introduces a very convenient unification of all coordinate systems for the spherically symmetric vacuum GR solution that manifest the static character ( of the exterior...
  41. H

    If doppler shift can be caused by gravity

    ... In other words a photon is energy-mass equivalent so it is effected by gravity. If the photon comes from a place of very high gravity, and we see it shifted, does the emitter have to be moving? ( this is a trick question. I'm heading to Mach's Principle :-) If high gravity can dopple...
  42. T

    Doppler Effect Homework: Source Moving Away from Observer

    Homework Statement A source of sound emits waves of wavelength λ, period T and speed v when at rest. The source moves away from a stationary observer at speed V, relative to the observer. The wavelength of the sound waves, as measured by the observer is A. λ + vT B. λ - vT C. λ + VT D...
  43. G

    Finding the speed of quaser using the Doppler equation

    Homework Statement The Hβ line of the hydrogen atom's spectrum has a normal wavelength λβ= 486 nm. This same line is observed in the spectrum of a distant quasar, but lengthened by 19.0nm . What is the speed of the quasar relative to Earth, assuming it is moving along our line of sight...
  44. J

    Doppler effect with two moving objects including wind

    Homework Statement An observer is moving to the right. A source is moving to the left. There is a wind moving to the right. What is the observed frequency? I had a quiz and this came up. I'm not sure if I did it right. Homework Equations f'=f(v±(vl-vw))/(v±(vs-vw)) The Attempt...
  45. T

    Doppler effect in matter waves

    If I have a matter wave (for example, electron waves in a electronic microscope) at a given wavelength λ, and I move with respect (towards) them at speed v, I will measure a Doppler shift in the wave given by: \frac{1}{{\lambda '}} = \frac{1}{{\lambda '}}\left( {1 + \frac{v}{{v_e }}} \right)...
  46. J

    Finding the speed of an approaching object using the doppler effect and sonar

    Homework Statement I attatched 2 images, the problem, and my work (including the formula needed)This "double shift" is what's getting me. Is it going 2% towards the object, and 2% from it? Or I'm I suppose to use 2 functions:F'=(f+xf) and F'=(f+yf) where x + y = 0.04? Homework Equations See...
  47. O

    Using the Doppler formula to find radial speed of a star

    Homework Statement High resolution spectroscopy reveals that the H line is located at a wavelength of 656.250 nm for this star. The wavelength of H measured in the lab is 656.280 nm. Calculate the line-of-sight velocity of the star. Homework Equations Here's the Doppler...
  48. C

    Is the only evidence for an expanding universe the doppler Red Shift?

    Basically, all more distant galaxies have a Red Shift that increases with the distance to the galaxy, the Universe is expanding. 1) If there are other pieces of evidence that indicate the Universe is expanding, what are they? 2) Any internet links describing exactly how the other...
  49. B

    Quick Question about the Doppler Effect

    Hi, I'm confused about how Doppler effect shifts the wavelength of light depending on the speed of the emitter. It makes sense from a classical point of view that the wavelength should shift. However, when I consider that light comes from photons, quantized energy, any shift in frequency...
  50. L

    Mass of Planet Using Radius and Doppler Effect

    Homework Statement Imagine you are observing a spacecraft moving in a circular orbit of radius 128,000 km around a distant planet. You happen to be located in the plane of the spacecraft 's orbit. You find that the spacecraft 's radio signal varies periodically in wavelength between...
Back
Top