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. R

    Doppler Effect 2 Homework: Calculating Distance of Police Car from Ambulance

    Homework Statement An ambulance is traveling at 84.0 km/h. The ambulance has a siren which produces sound at a frequency of 1.7 kHz. Assume the speed of sound in air is 345.0 m/s. A police car is traveling at a constant speed of 80.0 km/h directly towards the ambulance. The police car...
  2. R

    Doppler Effect of an ambulance

    Homework Statement An ambulance is traveling at 72.0 km/h towards an intersection. Jim stops his car to give way to the ambulance as shown in the diagram below. In the diagram, the angle θ = 41.0 °. The ambulance has a siren which produces sound at a frequency of 2.1 kHz. Assume the speed...
  3. matt_crouch

    Doppler effect wavelength from car

    Homework Statement A car is traveling at 30m/s in still air. the frequency of the siren on the car is 600hz. The velocity of sound in still air is 330 m/s. what is the wavelength of the sound waves a)directly in front of the car b)directly behind the car What is the frequency of the...
  4. X

    Doppler effect of submarines question. Please help

    Homework Statement A French and a U.S. submarine are moving directly towards each other during manoeuvres in still water. The French submarine is moving at 50.0 km.hr-1. It sends out a sonar signal at 1100.0 Hz. The frequency detected by the French submarine (reflected back from the U.S...
  5. P

    Submarine Distance - Hard Doppler effect

    Homework Statement A French and a U.S. submarine are moving directly towards each other during manoeuvres in still water. The French submarine is moving at 50.0 km.hr-1. It sends out a sonar signal at 1100.0 Hz. The frequency detected by the French submarine (reflected back from the U.S...
  6. J

    How Far Did the Stuntwoman Fall Based on Doppler Shift Analysis?

    Homework Statement A stuntwoman is preparing to take a punch, crash through a "candy glass" window, and fall a long distance. The script calls for her to emit a piercing scream just before she hits the "ground." In reality, she will land on a waiting airbag. Lights! Camera! Action! The...
  7. M

    Doppler effect on a police car?

    A police car's siren emits a wave with a frequency of 60 Hz. The speed of sound is 300 m/s and the car is moving 50 m/s. "what is the wavelength of the wave behind the car" So, the answer seems pretty easy. The observer is a stationary point behind the car, and the source is moving away...
  8. J

    Calculating Doppler Effect with Wind: 900 Hz Siren, 15.0 ms-1 Wind Speed

    Homework Statement A siren emits a frequency of 900 Hz. Wind is blowing at a steady speed of 15.0 ms-1. The speed of sound in calm air is 343 ms-1. What is the frequency heard by someone approaching at 15.0 ms¹, (i) when the wind blows from the person to the siren, and (ii) when the wind...
  9. S

    How Does Wind Affect the Doppler Effect in Jet Flight?

    Homework Statement Two jet airplanes are flying due east. The leading jet is flying at 1.3 times the speed of sound. The trailing jet is flying at 464 mph (both relative to the ground). The wind is blowing 182 mph due west. If the engine of the leading jet has a frequency of 2824 Hz, what...
  10. M

    How Does the Doppler Effect Alter Perceived Train Horn Frequencies?

    Homework Statement a train moves with uniform velocity . its horn is with a definite frequency . then if the frequency that a man in the station had heard is changed from 5400 Hz to 4500 Hz . calculate :- 1- velocity of train. 2- the real frequency of the source . let the velocity of sound...
  11. S

    Doppler effect and Resonance-relationship?

    Doppler effect and Resonance--relationship? we have a structure called Menar Jonban (i.e. Shaking Minaret-- it's basically a minaret that could be shaken --- literally!..you shake one minaret and the other one shakes too!) ... obviously the best explanation of the phenomenon is resonance .. but...
  12. A

    Cosmological redshift as a Doppler effect or metric evolution?

    In several threads where I've seen the redshift issue discussed there's been some confusion about this point, Must we treat cosmological redshift as a purely kinematic (relativistic)doppler effect or as the time dymamics of the metric space? Or both views can be made to converge?
  13. C

    Why You Can't Hear Doppler Effect in Car/Train Scenario

    Homework Statement -You are traveling in a car near a speeding train. The train whistle blows but you fail to hear the doppler effect. What conditions might prevent you from hearing it? Homework Equations The Attempt at a Solution -Ok, all I can come up with is that maybe...
  14. J

    Calculating Doppler Shift with Ship Sonar and Moving Targets

    Homework Statement The sound source of a ship's sonar system operates at a frequency of 23.0 kHz. The speed of sound in water is 1482 m/s. What is the difference in frequency between the directly radiated waves and the waves reflected from a whale traveling straight toward the ship at...
  15. R

    Doppler effect to distance without using time-of-flight; can this be done?

    Hey all, I'm a newbie here with a question regarding doppler shift. Before I ask, I only have a very basic understanding of the doppler effect. So, my big question is: can a doppler shift measurement be converted to the distance between the source and target, without using the time of...
  16. R

    Doppler Effect: Moving Observer riding on moving source With reflection off wall

    Homework Statement A bus is moving at 37.00m/s towards a wall. The sound from the bus has an original wavelength of 0.1500m. The sound from the bus reflects off the wall. What frequency sound does an observer on the moving bus hear from the reflection?? Homework Equations Moving Observer: fo...
  17. Q

    Relativity - Doppler effect in reflection from a moving mirror

    Homework Statement A plane mirror is moving at a uniform speed v away from the observer and a pulsing source of light of frequency f_0. What is the frequency of the light reflected in the mirror as seen by the observer? This isn't an actual homework question but I have a similar...
  18. M

    Doppler Effect, conceptual problems (3)

    Homework Statement a. A fire engine is moving at 40 m/s and sounding its horns. A car in front of the fire engine is moving at 30 m/s, and a van in front of the car is stationary. Which observer hears the fire engine's horn at higher pitch, the driver of the car or the van? b. A bat flying...
  19. U

    Frequency, Time, Wavelength = Doppler Effect

    Homework Statement A small homemade firework goes off 3 meters about the surface of the water where a person is diving. The diver is 10 meters below the surface of the water. (a). How much time passes from the instant the firework goes off until the diver sees it? (b). How much time...
  20. E

    Relativistic Doppler effect and relativity principle

    Let's say i am in a car traveling at 0.5c relative to a truck- which is at rest relative to the ground- approaching me from the opposite direction. Relative to me, the truck is going at 0.5c. Both, truck and car, frames of references are inertial frames of reference. Therefore, the principle of...
  21. L

    Sound and doppler effect on window pressure

    Homework Statement *See attached diagram* On straight, level, parallel tracks separated by a distance d, two trains are testing their horns (in still air of density ρair). The horns (located at the train fronts) emit equal frequencies. Horn 1 is a pipe, open at one end, emitting a total power...
  22. P

    Doppler effect when moving towards then past each other

    You are driving along a highway at 27.50 m/s when you hear the siren of an emergency vehicle traveling in the opposite direction on the other side of the highway. When the vehicle is approaching you, you hear the frequency of the siren as 2800 Hz, but when it is past you the frequency becomes...
  23. S

    Angular velocity, the Doppler effect, and frequencies.

    Homework Statement A speaker is attached to a wire 1.5 m long and is spun in a circle at 2 rev/s. The speaker is connected to an electric piano on which a child is playing a note at 261 Hz. Speed of sound in air is 343 m/s. What range of frequencies will the stationary observer hear? I...
  24. M

    Realistic explanation of the doppler effect

    Could anyone who knows give me a really simple yet realistic explanation of the doppler effect. This is one of those things that just boggles the brain so to speak.
  25. S

    Sound waves and the doppler effect

    Homework Statement A jet is flying horizontally from A to B. When the plane is directly overhead at B, a person on the ground (C) hears the sound coming from A. ABC is a right triangle in B. The angle BCA = 36 degrees. The average temperature is 20 degrees Celsius. If the speed of the plane...
  26. S

    The doppler effect and time dilation context

    I'm having a hard time understanding some things regarding the doppler effect. Please excuse my Microsoft paint diagram, I'm no artist. http://img686.imageshack.us/img686/3949/diagram.jpg http://img686.imageshack.us/img686/3949/diagram.jpg" Given this scenario, which...
  27. S

    Doppler Effect Wind: Frequency, Velocity, Wavelength

    Homework Statement An observer is in rest.A source of sound is in rest.A wind blows along the line joining the observer and the source.What all remain same in these: a.frequency b.velocity of sound c.wavelength Homework Equations f prime=f(v+w-vo)/(v+w-vs) Doppler effect The...
  28. M

    Solve for the Speed of a Car Using Doppler Effect - Homework Question

    Homework Statement A car speeds towards the outside wall with its horn sounding a frequency of 160 HZ. The sound waves reflected off the wall cause the driver to hear 8.0 beats per second. There is no wind and the speed of sound is 343 m/s. Find the speed of the car. Homework Equations...
  29. W

    Is the Doppler effect for atomic spectra a purely realistic effect?

    i am now studying the Doppler effect in a thermal atomic gas If an atom travels in velocity v along x direction at some time, it emits a photon in some direction the momentum of the emitted photon can be well approximated with the free one thus the momentum of the atom after the...
  30. W

    Is the Doppler effect for atomic spectra a purely realistic effect?

    i am now studying the Doppler effect in a thermal atomic gas If an atom travels in velocity v along x direction at some time, it emits a photon in some direction the momentum of the emitted photon can be well approximated with the free one thus the momentum of the atom after the...
  31. R

    Doppler effect fire truck siren

    Homework Statement Hearing the siren of an approaching fire truck, you pull over to the side of the road and stop. As the truck approaches, you hear a tone of 460 Hz; as the truck recedes, you hear a tone of 420 Hz. How much time will it take for the truck to get from your position to the fire...
  32. J

    Doppler Effect Investigatory Project

    Can someone give me an idea on our Investigatory project about Doppler Effect...? Our project shouldn't be amounting in an expensive one. I am only 4th year high school student and so confuse what project will i make... Please Help me guys. Thanks in Advance Guys!
  33. C

    Doppler effect, offset from line of effect

    sorry lots of reading but i wanted to explain what I've done (tried to do) Homework Statement An ambulance has a loud siren, which emits a pure note at 5100Hz. A man 20 m from a straight road along which the ambulance is travelling, and records the frequency of the sound he hears from the...
  34. C

    Doppler effect, moving car and whistle

    Homework Statement Sally is a police officer who is standing in an intersection. A car driven by David approaches the intersection at a speed of 75 km/h. Sally blows her whistle (at a frequency of 900 hz) and signals the driver to stop. What does frequency does David hear? (speed of sound is...
  35. S

    Calculating Doppler Effect: Car Speed and Frequency Analysis

    Homework Statement A car is approaching a reflecting wall. A stationary observer behind the car hears a sound of frequency 745 Hz from the car horn and a sound of frequency 863 Hz from the wall. 1. How fast is the car traveling? A. 25.2 m/s B. 33.4 m/s C. 18.9 m/s D. 54.2 m/s 2...
  36. F

    Advanced Doppler effect questions

    1. The problem statement 1) A train whistle has a frequency of 1000 Hz. If the train is speeding at a velocity of 60 km/h past a stationary railroad crossing attendant, what is the apparent frequency a) as the train approaches him, b) as it moves away from him? Assume speed of sound to be...
  37. F

    Dog demonstrates doppler effect with squeaky toy

    lol :-p http://improbable.com/2009/11/13/doppler-effect-with-a-dogs-squeak-toy/
  38. M

    Calculating Doppler Effect: Bat Approaching Wall at 10 m/s & Squeaking at 80 kHz

    A bat is approaching a wall. If it is traveling at 10 m/s and squeaks at 80 kHz, what frequency does it hear in its echo? f=fo(1 +/- vo/v) f=fo (1/(1 +/- vs/v)) So I got the right answer by initially making the wall the stationary "observer" and the bat the moving source, and finding...
  39. M

    Calculating Doppler Effect: Bat Approaching Wall at 10 m/s with 80 kHz Squeak

    A bat is approaching a wall. If it is traveling at 10 m/s and squeaks at 80 kHz, what frequency does it hear in its echo? f=fo(1 +/- vo/v) f=fo (1/(1 +/- vs/v)) So I got the right answer by initially making the wall the stationary "observer" and the bat the moving source, and finding...
  40. N

    Does Doppler effect change the energy of emitted light?

    A very basic question (I hope this is the right place for it). A distant star emits, say, a high-energy x-ray. Due to expansion of space, this reaches us as visible light (say, red part of the spectrum). The light that reaches us has less energy per photon (E=h*nu) then the light emitted...
  41. K

    Relativity_velocity addition and doppler effect

    Homework Statement The Enterorise NCC1701 is cruising 0.6c above the moon of Eridani when it spots a Klingon warbird sunwards. i. It fires a proton torpedo at speed 0.75c relative to the ship at the Klingon warbird. Assuming the proton torpedo does not accelerate, at what velocity must the...
  42. J

    How can the Doppler effect of light determine an astronaut's speed?

    Homework Statement An astronaut is said to have tried to get out of a traffic violation for running a red light (lambda= 670nm) by telling the judge that the light appeared green (lambda= 540nm) to her as she passed by in her high powered transport. If this is true, how fast was the astronaut...
  43. A

    Doppler Effect radio broadcasting

    Homework Statement Three radio-equipped plumbing vans are broadcasting on the same frequency f_0. Van 1 is moving north of van2 with a speed of v, van 2 is fixed, and van 3 is moving west of van 2 with a speed of v. What change in frequency (f-f_0) does van 3 hear from van 1? Homework...
  44. O

    The Doppler Effect of radar gun

    Homework Statement You are in charge of calibrating the radar guns for a local police department. One such device emits microwaves at a frequency of 2.15 GHz. During the trials, these waves are reflected from a car moving directly away from the stationary emitter. You detect a frequency...
  45. H

    How Does Source Motion Affect Frequency in the Doppler Effect for Sound?

    we know...when a source is running towards the listener...the wavelenth of sound become small and number of waves inceases...as far as i know ..the logic behind is..when a source runs..then waves become congested in a small distance between source and listener...it is so far so ridiculous to me...
  46. ideasrule

    The Flyby Anomaly: Ranging Data, Transverse Doppler Effect

    One paper claims that the flyby anomaly only exists because NASA scientists forgot about the transverse Doppler effect. If that's true, why is it still called an anomaly? Why isn't everyone banging their heads on walls and thinking, "D'oh! I can't believe I forgot about that!"? If it's not...
  47. A

    Doppler Effect: How Does the Ambulance Siren Vary?

    When an ambulance approaches, its siren sounds shriller than when I relatively motionless to it, and vice versa. Such is an example of doppler effect, isn't it? However, there one thing I am not sure: does the siren gradually becomes more shriller when the ambulance approaches, or not...
  48. M

    How to Calculate Buoyant Force and Volume of a Submerged Object?

    doppler effect quick question! Homework Statement An ambulance traveling at speed 31 m/s is producing a loud sound of frequency 895 Hz. You see the ambulance in your rear view mirror as the ambulance approaches you and you slow down to 14 m/s as a law obeying citizen (hehehe we know now)...
  49. S

    Doppler effect of an ambulance

    Homework Statement An ambulance is running on an expressway at a speed of 60 km/h from east to west (from A to B) with a siren of 880 Hz. Let the frequency of the siren sound detected by an observer located at a point O be Va and Vb when the vehicle just passes point A and point B respectively...
  50. P

    Energy loss in the doppler effect?

    If the energy of an EM wave = h x f and when a light emitting body (of a particular power) is moving toward or away from the observer the observed frequency changes, does the energy change? If so where does the gained or lost energy come from?
Back
Top