What is Doppler effect: Definition and 505 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. H

    Radar Doppler Effect: What Does the "V" Stand For?

    in the equation at: http://en.wikipedia.org/wiki/Radar#Doppler_effect what does the v stand for? it is not explained, only vobs and vs are explained. Thanks.
  2. L

    How to Calculate Distance Using the Doppler Effect

    Homework Statement A physics student drops a vibrating 421 Hz tuning fork down the elevator shaft of a tall building. The temperature in the shaft is 20 °C. When the student hears a frequency of 392 Hz, how far has the tuning fork fallen? fS = 421 Hz fL = 392 Hz VSOUND = 343 m/s...
  3. L

    How Does the Doppler Effect Alter Perceived Siren Frequencies at a Junction?

    Homework Statement A car stops at 50m to a road-railway junction. A train is moving with a constant velocity 35m/s towards the junction. If the train emits a siren at a frequency of 100Hz, calculate the maximum and the minimum frequency that can be heard by the car driver. velocity of...
  4. L

    Doppler effect and some doubts

    Homework Statement Revered members, I have attached the image of Doppler effect explanation. Homework Equations I have the following doubts 1)t1 = L/v 2) t2 = T0 +( L + vsT0)/v But why T0 comes here, instead of ( L + vsT0)/v The Attempt at a Solution
  5. P

    Doppler Effect (Proving equal wavelengths )

    Hi, I am doing doppler effect and this question wants me to prove that the wavelength perceived by the observer and that of the wave emitted is the same. I tried doing it but couldn't, so I checked out what they had as an answer: They said that the wavelength of the emitted wave is: v...
  6. K

    Question on a doppler effect problem and equation

    Homework Statement Question: Two trains on separate tracks move toward one another. Train #1 has a speed of 130 km/hr and train #2 a speed of 90km/hr. Train 2 blows its horn, emitting a frequency of 500 Hz. What frequency is heard by the engineer on train #1? Homework Equations This is...
  7. A

    Understanding the Doppler Effect in Space-time Curvature

    I have a question that has been bugging me for a while. You see, I have a predisposition of trying to visualize everything that I learn. I have no problem visualizing space-time, black-holes distorting space-time, the universe expanding, etc..., but when it comes to the Doppler Effect I want to...
  8. S

    Non-symmetric nature of the Doppler Effect with sound

    While studying the Doppler effect at school, it struck me as strange that the following two problems have different solutions: a) you are moving at 40 m/s toward a source that is making a sound with a frequency of 1000 Hz. What frequency do you hear? (speed of sound= 340 m/s) b) The...
  9. Y

    Doppler effect car horn question

    Homework Statement A policeman with a very good ear and a good understanding of the Doppler effect stands on the shoulder of a freeway assisting a crew in a 40-mph work zone. He notices a car approaching that is honking its horn. As the car gets closer, the policeman hears the sound of the...
  10. O

    Does the amplitude of a wave change with the Doppler effect in a medium?

    Does the amplitude of a wave changes when the source is moving? I am mainly interested in waves in a medium (e.g. sound, water...) No text about Doppler effect I have found mentions anything about the amplitude so I guess it does not change. However in the case if the speed of the source...
  11. B

    Frequency Shifts: Doppler Effect & Wavelength

    Frequency changes relative to the observer due to the doppler effect. Does wavelength?
  12. L

    Determining Distance from Release Point Using Doppler Effect

    Homework Statement A tuning fork vibrating at 506 Hz falls from rest and accelerates at 9.80 m/s2. How far below the point of release is the tuning fork when waves of frequency of 488 Hz reach the release point? (Take the speed of sound in air to be 343 m/s).Homework Equations...
  13. A

    What is the perceived frequency of Bird B when it hears Bird A's screech?

    Homework Statement Bird A and B are flying towards each other Bird B at 20m/s Bird A at 15m/s and screeches with a frequency of 3200 Hz what does bird B perceive? Homework Equations the speed of sound is 343m/s Fobserver==Fsource((vsound+vobserver)/(vsound+vsource) The Attempt...
  14. L

    Speed of light is constant because of doppler effect?

    Doppler effect told us that the frequency and wavelength changed but not the speed of wave if the transmitter or receiver is moving. Could I interpret Doppler Effect as follow: Frequency/wavelength change for different observers, however, the speed of wave is constant for all observers. If...
  15. T

    Doppler Effect physics homework

    So a factory whistle emits a sound at 875Hz. The temperature of the air is 25.9oC. What frequency will be heard by an observer in a car traveling at 27m/s away from the source i know this is a two step problem but i have no idea where to start! anyone lead me in the right direction?
  16. T

    Doppler Effect Observed Frequency Under Special Conditions

    vw= Velocity of Wave vm= Velocity of Wave Source fw= Frequency of the Wave fd= Frequency of the Wave relative to Detector as Wave Source is also moving q= Infinity For the wave frequency detected by a detector at rest as the wave source* is moving towards it, there is: fd=( vwfw )/(...
  17. S

    Doppler Effect involving two moving objects

    Homework Statement A truck moving at 36 m/s is overtaken by a police car moving at 45 m/s in the same direction. If the frequency of the siren relative to the police car is 500 Hz, what is the frequency heard by an observer in the truck as the police car approaches the truck? (The speed of...
  18. J

    The Doppler Effect: Near and Far Galaxies

    I found a question in a Maltese physics past paper dealing with the doppler effect. I managed to figure out the part dealing with the effect of motion of the wave source, but i was asked this: How does The Doppler Effect show us the difference between galaxies that are near and those that are...
  19. A

    Doppler Effect of light ; and electric , magnetic fields

    my query is : The electric and magnetic fields don’t squeeze or stretch then how is Doppler Effect of light possible? In the phenomenon of Doppler Effect, light emitted from a moving source is detected to have different frequency. If this is taken on terms of detecting the no. of waves...
  20. S

    Calculating Frequency Difference of a Rotating Siren - How Fast Must It Spin?

    Homework Statement A siren has two loud speakers attached to a rotating disk. The disks radius is 3m. The speakers emit a sound frequency of 300 Hz.(Speed of sound in air is 344 m/s) A)How fast does the disk need to spin for an observer standing some distance away to perceive two frequencies...
  21. K

    Are the forces of gravity subject to the Doppler effect?

    Was it considered that the force of gravity could vary according to the redshift equation? 1+z=\frac{1+v \cos (\theta)/c}{\sqrt{1-v^2/c^2}} If those who consider this are right, then it would imply that an object leaving a gravitational system would experience a slight decrease in the...
  22. T

    Doppler Effect: can light waves have different effects, depending on your speed?

    I have a question about of light waves. Moving at high speeds toward or away from visible light could be the difference of experiencing that light as violet or red. Of course this experience is due to the photoreceptors in the eye seemingly experiencing a shorter or longer wavelength. My...
  23. M

    Doppler Effect, Stationary source moving observer

    Homework Statement My books states, considering a stationary source emitting waves at frequency f, such waves having velocity v, and an observer approaching the source along a linear path at velocity vO we have that: The observer registers the velocity of the waves at v+v0. Up until now all...
  24. A

    Speed of Cars with the Doppler Effect

    Homework Statement Two cars traveling with the same speed move directly away from one another. One car sounds a horn whose frequency is 185 Hz and a person in the other car hears a frequency of 173 Hz. What is the speed of the cars? Homework Equations The Doppler Effect. The...
  25. S

    The Doppler Effect For EM Waves

    Homework Statement A star is moving away from Earth at a speed of 2.4 x 10^8 m/s. Light of wavelength 480 nm is emitted by the star. What is the wavelength as measured by an Earth observer?Homework Equations fo=fs(1 - vrel/c) I substracted because they the star is moving away from the earth...
  26. X

    Solving for Vv= The doppler Effect

    The problem: I have to answer a question about the Doppler effect using the formula attached. I know i have to solve for Vw, but I get Vw/Vw=(Fd/Fs)(-Fs) and I am possitive that's not right, can someone please help me out?? Thankyou
  27. K

    How Does the Doppler Effect Calculate Submarine Depth and Velocity?

    A stationary destroyer is equipped with sonar that sends out pulses of sound at 30.000 MHz. Reflected pulses are received from a submarine directly below with a time delay of 60 ms at a frequency of 29.958 MHz. (a) If the speed of sound in seawater is 1.55 km/s, find the depth of the...
  28. J

    The Doppler Effect: Deducing an Expression for Frequency

    Homework Statement A sound source moves at a constant velocity. A listener is standing at a distance L away from it. Given that the source moves in a straight line at a right angle to the listener and starts closest to the listener (ie at t=0) deduce an expression for the frequency heard by the...
  29. K

    Doppler Effect: Wavelengths of Sound Waves

    Homework Statement I read that when a body approaches a stationary one which emits radar waves, the wavelength λ2 of the returned waves is longer than λ1, the wavelength of the emitted ones, but I get the opposite. I suppose this is true for sound waves also. See picture. The Attempt at a...
  30. B

    How Fast is the Ambulance Traveling in the Doppler Effect Problem?

    Homework Statement You are traveling north of wayne rd at 20.0m/s, when you notice an ambulance in the distance approaching you at a high rate of speed. Using an iPhone app, you measure the siren's frequency to be 1.427 kHz. From previous experience you know that the ambulance siren emits a...
  31. M

    Doppler Effect- small question on formula setup.

    Homework Statement The security alarm on a parked car goes off and produces a frequency of 958 Hz. The speed of sound is 343 m/s. As you drive toward this parked car, pass it, and drive away, you observe the frequency to change by 95 Hz. At what speed are you driving? Homework...
  32. Terocamo

    Why Do Equations for Doppler Effect Differ for Moving Source and Observer?

    I have just read about the principle of Doppler effect. However there is a point which seemed a bit tricky. According to the book, when the source of wave is moving the apparent frequency to a stationary observer is given by the equation: f'=true frequency*speed of wave/(speed of wave +...
  33. K

    Michelson interferometer and Doppler effect

    Homework Statement Hello, I'm working on an experiment that involves a Michelson interferometer and doppler effect. Here is the description of the apparatus. Michelson interferometer is set up with one moving arm and microwave is transmitted and received. With the beam splitter splitting...
  34. A

    Doppler Effect Homework: Find Speed of Ambulance

    Homework Statement A stationary observer at a crosswalk hears an ambulance siren with an apparent frequency of 480 Hz when the ambulance is approaching. After the ambulance passes the apparent frequency is only 420 Hz. Find the speed of the ambulance. Assume v = 343 m/s for the speed of sound...
  35. A

    Temperature from Doppler Effect spectral broadening

    Homework Statement A doppler effect problem: A sodium atom is emitting radiation at a wavelength of 6000 angstroms. When measured however the wavelength is widened to 6000 +/- 0.02 angstams. If this is primarily due to the doppler effect, what is the temperature of the sodium atom...
  36. DaTario

    Clear explanation of Doppler effect assimmetry

    Hi All, I would like to know how can one explain the assimmetry in Doppler effect. I will illustrate what I mean. If a source emits 440 Hz but is coming in my direction with a velocity V (measured in m/s) I will hear, let's say, 441 Hz. Now, if the source is at rest with respect to the...
  37. Z

    Doppler Effect with acceleration Problem

    Homework Statement A source S and a detector D are initially at a distance of x=1km. Both start moving towards one another with same acceleration a = 10m/s2. Frequency of source is f = 2000Hz. Find the frequency observed by the detector at time t=4s. Speed of sound in air is v=300m/s The...
  38. H

    Doppler effect and the twin paradox

    Hi. I am learning special Relativity and I am seeing that the answer to the twin paradox involves the Doppler effect, and I am struggling to understand what is going on. First let me explain what I know about the Doppler effect. If an object produces waves (might it be light waves or sound...
  39. I

    The Theory of the Transverse Doppler Effect

    I'm doing a night course in General Relativity and we're currently finishing off Special Relativity... We're working mainly off of D'Inverno. We've just covered the relativistic doppler effect and some associated things like aberration. When it came to talking about the transverse doppler...
  40. G

    Exploring the Doppler Effect in Sound, Light & Water Waves

    Does Doppler effect exhibit in sound waves, light waves and the waves on the surface of the water?
  41. kreil

    How Does the Relativistic Doppler Effect Apply on a Rotating Disk?

    Homework Statement A source and detector are placed a certain angle \phi apart on the edge of a rotating disk. The source emits radiation in all directions at a frequency \omega_* in its instantaneous rest frame. What frequency is the radiation detected at? (Hint: Little information is...
  42. B

    Doppler effect of light spectrum

    When we first realized that the further away a galaxy is the further towards the red side of the spectrum it was, we beleived this to be do to the expansion of the universe? Wouldn't it have been simplier to say that the further away a galaxy was the further the wave function stretched over...
  43. M

    Solving Bat Doppler Effect Homework Problem

    Homework Statement A bat, flying at a constant speed of 19.5 m/s in a straight line toward a vertical cave wall, makes a single clicking noise and hears the echo 0.15 s later. Assuming that she continued flying at her original speed, how close was she to the wall when she received the echo...
  44. F

    Doppler effect for light - how can it be explained ?

    Did u ever try to explain Doppler effect for light in depth, at the photon level ? I'm no scientist. I'm trying to find a visual or mental representation of the doppler effect for electromagnetic waves. There is no medium to vibrate. No way I can understand the phenomenon by making a...
  45. A

    Planck relation, relativistic doppler effect, and relativistic mass

    I've been trying to graph an idea I had, but frankly I don't understand SR well enough to ensure my assumptions are correct, and that I'm using the correct formulas. I would appreciate any input/corrections you folks could give. Here's the idea, which I'll follow with my assumptions: Idea...
  46. fluidistic

    Calculating Relativistic Doppler Shift for Moving Radar

    Homework Statement A car is getting closer to a radar as a speed of 135 km/h. If the radar works at a 2 \times 10 ^{9} Hz, what difference of frequency is observed for the radar?Homework Equations \mu=\frac{\mu _0 \sqrt {1- \frac{v^2}{c^2}}}{1-\frac{v}{c}}The Attempt at a Solution I converted...
  47. K

    Are forces subject to the doppler effect?

    I know that photons hitting a solar sail can add energy to that sail. I know that photons are gauge bosons. I know that gauge bosons are thought to be the carriers of fundamental forces. If a solar sail were gaining speed to a point where it reached relativistically with respect to the power...
  48. F

    What is the Doppler Effect and When Does it Occur?

    Homework Statement Firstly, whilst reading all this more complicated (and far more interesting) physics in other threads I feel like a dunce posting something which is probably of 'lower' level here as it were, but here goes: If we have a vehicle like a police car (with siren going) moving at...
  49. L

    High School Physics: Doppler Effect

    Homework Statement An automobile is approaching you at a speed of 60.0 km/h and sounding its horn. The fundamental frequency of the horn sounds to you like 388 Hz. If the real fundamental frequency of the horn is 369 Hz, what is the speed of sound? Homework Equations Doppler...
  50. N

    Do gravity waves experience doppler effect?

    Will gravity waves theoretically experience a doppler effect for bodies in relative motion to the source?
Back
Top