Doppler Definition and 749 Threads

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.

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  1. Q

    Is the Doppler shift an independent principle?

    Is the Doppler shift an independent principle of wave mechanics? Or we can deduce it from other principles of wave mechanics? The article [1] gives an analogy of throwing and receiving balls. But it may be inappropriate. We are discussing wave mechanics? Why bother an analogy of balls/particles...
  2. N

    Derivation of the Relativistic Doppler Effect

    I'm working through the derivation found on this site: http://maths.dur.ac.uk/~dma0cvj/mathphys/supplements/supplement5/supplement5.html And though most of it is clear to me, I stumbled upon a little problem. My question is about the section that starts with "This is all according to...
  3. F

    Astronomy and the Relativistic Doppler Shift

    Homework Statement The hydrogen atoms in a star are also moving at high velocity because of the random motions caused by their high temperature. As a result, each atom is Doppler shifted a little bit differently, leading to a finite width of each spectral line, such as the 656.46-nm line we...
  4. D

    Localization by the doppler effect

    I have heard that if one is hypothetically placed in a box completely solid, whith a shield that leaves everything that would have entered a normal box, like light, or neutrinos, out of it. If you sent that in a certain speed, with nothing affecting it, just traversing through space, the person...
  5. K

    Understanding the Doppler Effect: Using c-v0, c+v0, c+Vs, c-Vs

    can someone pleasezz explain the dopplers effect n when to use the c-v0 , c+v0 ,c +Vs ,c-Vs etc etc in the formula in the pic thnx a lot in advance
  6. D

    Doppler Effect of Light Waves at Half Speed?

    I cannot search the forum to check if this has been posted before, because I do not know what it is called in english... That means that i have to try to explain what i means, here it goes: When a light producer, like a star is moving, it sends out waves that is either compressed or expanded...
  7. V

    Doppler effect star and earth question

    Hello I have a question that is giving me trouble: Light of wavelength 659.7 nm is emitted by a star. The wavelength of this light as measured on Earth is 661.1 nm. How fast is the star moving with respect to Earth? km/s Is it moving toward Earth or away from it? Here's where...
  8. P

    What is the Period of the Sun's Rotation Based on Doppler Shift of Light?

    I have to calculate the suns period time, when given the following information; "The H_{alpha} line has the wavelength \lambda_0 = 656.1~nm . Measuring this spectrum from opposite sites of the suns equator, shows that there is a difference between that is \Delta \lambda=9\times 10^{-12}~m ...
  9. S

    Does Motion Affect Frequency in Sound Waves?

    Hello, The reason for the shifting of freqeuncies of all types of waves in response to relative motion away or towards the center of propagation, is caused by a corresponding stretching or compressing of the medium, correct? I mean for sound, if one moves toward the place where the sound...
  10. Q

    What causes a sonic boom when traveling at Mach 1+?

    Here's a problem that's been bugging me. We know that we get sonic booms because of the Doppler effect since, for an example, the jetplane over takes the soundwaves that it emits some time ago because it is travels faster than the speed of sound. The overlapping of new sound waves it produce...
  11. M

    Deriving Doppler Shift Using Spacetime Diagram

    Alright, I'm trying to derive the dopper shift using a spacetime diagram (see attached). If we model light pulses then we can derive the distance between the pulses in time, and hence the doppler shift... right? So, if we make some light pulses along some sort of time event in the x, cT frame...
  12. R

    Bat echolocation - doppler effect

    Hi, this is the question: ------------------------ A bat flies toward a wall, emitting a steady sound with a frequency of 22.5 kHz. This bat hears its own sound plus the sound reflected by the wall. How fast should the bat fly, v_b, to hear a beat frequency of 225 Hz? Take the speed of sound...
  13. B

    What is the relationship between the Doppler effect and proper time?

    defining the Doppler Effect as: "what we have to compare in a Doppler effect experiment are the period at which light signals are emitted measured in the rest frame of the source and the period at which they are received by an observer measured in its rest frame" we are doing a good job...
  14. M

    Doppler effect ambulance problem

    Question: An ambulance with a siren emitting a whine at 1300 Hz overtakes and passes a cyclist pedaling a bike at 2.44 m/s. After being passed, the cyclist hears a frequency of 1280 Hz. Use 343 m/s for the speed of sound in air. How fast is the ambulance moving? i set up the doppler equation...
  15. F

    The effect of the medium on doppler shifts

    hello, this has stumped me and i think there is something weird going on my definition of reference frames: lets look at two scenarios: scenario1:sound emitter and observer are both moving with velocity x in the same direction in a stationary medium... no doppler shift is expected...
  16. A

    Determining Velocity of a Police Car Using the Doppler Effect

    Please help me: . While standing at a crosswalk, you hear a frequency of 630 Hz from an approaching police car. After the police car passes, its frequency is 430 Hz. What is the velocity of the police car? (speed of sound in air = 343 m/s)
  17. R

    Doppler Effect Project: Exploring Experiments & Ideas

    Hi - I'll keep this relatively short. I'm doing an investigation into the doppler effect and I need to do a series of 3 to 5 experiments in order to prove/show something. At the moment I am a little lost as to what I could experiment into regarding the doppler effect, and how to go about it in...
  18. G

    Is Cross-Posting Allowed on PF Forums?

    A friend and class-fellow of mine(B.B. Gupta) came up with the following interesting problem(during the starting days of our M.Sc.):-There's a photocell and a (monochromatic)source of light at a certain distance from the photocell.The source of light emits light of frequency lower than what is...
  19. F

    Doppler Effect Police Car Question

    For this problem, I used the Doppler Effect equation, and got 419.361 as my answer. I used + on the top and - on the bottom. Do I need to switch the two?
  20. H

    Does Wind Affect the Doppler Effect on Sound?

    Im trying to find the ansewr to an extra credit question in class. We are studing the doppler effect and the question came up does wind effect the sound you hear. At first i was thinking that it might but since the velocity of sound is so much greater than that of wind that you would notice no...
  21. E

    Two Doppler Shifts: 800Hz to 126Hz

    A stationary source directs an 800-Hz sound wave toward an approaching object moving with a speed of 25.0 m/s. What is the frequency shift of the reflected wave if the air temperature is 20ºC? (Hint: There are two Doppler shifts here. Why?) f = 800Hz the speed of sound = v = 331 + 0.6Tc =...
  22. E

    Is there a Doppler effect when sound source and object move at right angles?

    "Is there a Doppler effect if a sound source and an object are moving at right angles?" I assume this means that both are moving away from a single point... I thought there would be a Doppler effect because both objects are moving and therefore the sound produced has an effective longer...
  23. A

    Doppler Shift/Wien's Law/Hubble Constant Problems

    1.) If the actual value of the Hubble Constant is determined to be 72.3517 km/sec/MPC, what would this give for the age of the Universe? * Could I possibly use V= H*D to find what the age of the universe is. 2.) What would be the Wien's Law predicted wavelength for an accretion disk heated...
  24. N

    How Far Does a Motorcycle Travel When Hearing a Siren at 90% Frequency?

    a motorcycle starts from rest and accelerates along a straight line at 2.81m/s^2. the speed of sound is 343 m/s. a siren at the starting point remains stationary. how far has the motorcycle gone when the drive hears the frequency of the siren at 90.0% of the value it has when the motorcycle is...
  25. G

    Doppler Effect change in the frequency Question

    Hey guys, Im having lots of problems with this question.. A car moving at 40m/s and a truck moving at 15m/s travel along the same straight road. The car's horn has a natural frequency of 400Hz. What is the change in the frequency observed by the truck as the car passes the truck? Assume the...
  26. M

    What Is the Velocity of the Shuttle Relative to Earth?

    This is the problem A shuttle is launched from a space station and travels away from it in a straight line. It rapidly accelerates and obtains a steady velocity of v = 4c/5 relative to the space station. The spaceship sends out radio signals of a frequency f. The spaceship is on a mission to...
  27. G

    How can I derive the relativistic Doppler formula?

    I have a simple question about a relativistic Doppler effect problem. To keep the math simple, I have intentionally left out the labels, you can view the speed of light as 300 miles per seconds, or 300 meters per second, it isn’t important. Speed of light = 300 per second Wavelength of...
  28. B

    The Doppler Effect and Electromagnetic Waves

    I had a question. I did a problem where a distant galaxy emitted light that had a wavelength of A. On earth, the light had a wavelength of B. B ended up being greater than A. The question asked if the galaxy was receding from the Earth or approaching the earth. The answer turned out to be the...
  29. B

    Aetherists and the doppler effect

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  30. M

    Calculating Up-Doppler with 600nm Laser Scanning at 55m/s | Mega Sig Figs

    Okay, I don't need an answer . . . I just need to know how I would go about getting an answer. Here is the question, exactly worded as on my worksheet: "What is the up-doppler for a 600.0 nanometer laser scanning an innocent, law-abiding, safe-driving, tax-paying, completely innocent...
  31. L

    Why is Direct Detection of Doppler Frequency Shift Impractical in Laser Doppler Anemometry?

    I am doing an experiment in the lab at the moment on laser doppler anemometry and a few questions have popped into mind, was wondering if anyone had any ideas/insights on them: Direct detection of the Doppler frequency shift using conventional prism or grating spectrometers is not usually...
  32. C

    The Doppler Effect: How Source & Listener Motion Affect Wavelength

    Why does the wavelength of the wave change when source is moving but not when listener moves?
  33. B

    What is the expression for the spectrum of a hot gas with Doppler broadening?

    Hi, A very hot gas is enclosed in an oven with a small window. The gas molecules emits radiation at a characteristic wavelength. I assume that because of the thermal motion of the molecules the emitted wavelengths will form a spectrum of some kind (Doppler broadening.) I am trying to derive...
  34. G

    Can the Doppler Formula be Used for an Accelerated Sound Source?

    Can i use the doppler formula ( i.e f = f(0){(v(+/-)v(0))/(v(+/-)v(s))}) when the source is accelerated taking v as the speed of sound in air v(o) the speed of the observer and v(s) the speed of source at the time the sound wave is generated . I tried deriving this formula but came across some...
  35. A

    How Does the Doppler Effect Alter Wavelength as a Train Approaches?

    1.) Suppose the sound from an approaching train whistle normally has a frequency of 1200 cycles per second, but the train is approaching at 50 meters per second. How would the Doppler Effect change the wavelength of the sound? (speed of sound 335 meters per second; I would like a quantitative...
  36. D

    Understanding the Doppler Effect Equation: Velocity and Frequency Relationship

    Suppose a person is traveling towards a wall with a tuning fork at frequency 'f' at a speed of 'v*'. Using the doppler effect equation: f' \ = \frac{v + v_o}{v - v_s} What would the sign of v_o and v_s be? I don't understand, since the man is both the observer and the source. (Let - be...
  37. Pengwuino

    What is the relativistic doppler shift in a multi-dimensional scenario?

    I have a problem here. I stole me a grad student and he didn't really know what to do either. Without further adoo (or whatever), i give you... the problem! There are 3 trucks transmitting on the same frequency. #2 is stationary. #1 moves to the left at velocity v. #3 moves up at velocity v...
  38. B

    Calculating Frequency Shift in the Doppler Effect for Submarine Sonar Waves

    I'm working on the following problem: Two submarines are underwater and approaching each other head-on. Sub A has a speed of 4 m/s and sub B has a speed of 18 m/s. Sub A sends out a 1010 Hz sonar wave that travels at a speed of 1522 m/s. The question asks two questions, but I'm stuck on...
  39. I

    Doppler Radar - Bandwidth, Continuous Wave or Pulse?

    Doppler Radar?? Please can someone help me with doppler radar...need to know bandwidth?? Is it usually continuous wave or pulse?? or can it be both?? pretty much just after some general knowledge on doppler radar? thanks in advance!
  40. Hydr0matic

    Doppler Effect in Accelerating Frames vs Normal Doppler Effect

    What is the difference in magnitude between the effects of normal doppler effect and doppler effect in accelerated frames, e.g. when the (light)source is accelerating wrt the observer? What is the formula for doppler effect in accelerating frames?
  41. N

    Doppler Effect: Finding Frequency vs Time

    Hi. I am doing a project about the Doppler Effect and I was wondering if someone here could help me. I have a tone source and I need to find the frequency with respect to time. I could use my mp3 player to record this frequency, which will then save it as a .wav file. I was wondering if...
  42. N

    Can a galaxy have a recession velocity greater than the speed of light?

    Hi all. I was reading: http://www.astro.ucla.edu/~wright/doppler.htm but I'm failing to understand this part: My understanding is that a galaxy cannot move faster than c (the speed of light). Why then could a galaxy moving close to c have a recession velocity greater than the speed of light...
  43. K

    How does Doppler affect the observed period of a moon of Jupiter?

    Question: The variable period of a moon of Jupiter, which is the basis of measurement of the speed of light in Roemer's method (whoever he is), is regarded as the Doppler affect. The period of the orbital motion of one of Jupiter's moons is approximately 42.5 hours; the speed of light is...
  44. L

    Distance Earth-Saturn: Solving the Doppler Effect

    I need to find what the distance between Earth and saturn would be if they were both in a straight line with the sun (both on the same side of the sun). The problem I'm trying to solve involves the doppler effect, and I can work it out if I know that distance. Does anyone know what it is...
  45. C

    Is this a doppler effect problem?

  46. D

    How Do You Calculate Motorcycle Speed Using the Doppler Effect?

    I'm having trouble solving this one: Two motorcycles are traveling in opposite directions at the same speed, when one of the cyclists blasts her horn, which has a frequency of 544 Hz. The other cyclist hears the frequency as 563 Hz. If the speed of sound in air is 344 m/s, what is the speed...
  47. Q

    How Does Relative Position Affect the Doppler Effect?

    Hi, I was wondering if anybody knows where I can find a good website that explains the Doppler Effect in terms of the position of the source and observer. I understand how the effect works, just not with relative position. (ie: when the velocity is positive...) Or Problems such as these...
  48. P

    Derivation of Doppler Effect Equations

    Hey, I need a bit of help with the derivation of Doppler's equations as shown in the attached image. (From Fundamentals of Physics) The paragraph where it states "Now let us again consider the situation..." I don't understand why they use vt + vDt I mean, the sound wave would initially have...
  49. W

    How to Calculate Doppler Effect Frequencies for Moving Objects?

    I've got 2 qns 1) Student holding a tuning fork vibrating at 440Hz walk away from a wall with a speed of 1.2m/s. What's the freq of the echo the student can hear from the wall? Speed of sound is 330m/s Can i just use Freq= [(330-1.2)/(330+1.2)] (440Hz) to solve 2) A car traveling at 10m/s...
  50. D

    Kepler's 3rd Law and the Doppler Effect

    Question: Imagine a space probe has been placed in a circular orbit about a distant planet. The probe emits a continuous radio signal with a wavelength of 8 m. You measure the signal from earth, and find it to have a wavelength that varies regularly between 7.99943 m and 8.00057 m, with a...
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