Describe the Doppler effect

Answer 1

VROOOOOOOMMMM! The change in pitch when a car speeds by, first higher (when approaching) then lower (when receding).

The Doppler effect is the term we give to the apparent change in frequency of waves (often light or sound waves) as the distance between the source and the observer changes. If either the source or the observer of a wave is moving so that the effect is that they are getting farther apart or closer together, the Doppler effect will appear. Let's look more closely.

If the distance between the observer and the source of a wave is decreasing because they are closing in on each other, something happens. The wave, which is normally characterized by a given frequency and an associated wavelength, will appear to increase in frequency (and decrease in wavelength). Let's get even closer and break it down a bit to see what happens.

When a wave reaches at an observer, it has a given wavelength. If there is no change in the distance between that observer and the source that wavelength remains constant. But if the distance of separation is decreasing (say if the sensor - observer - moves towards the source 8motion is relative so it does not matter which of the source or sensor moves relative to any frame of reference), as the crests and troughs of the wave arrive the observer will be (apparently) "running towards the next peak or trough" of the wave. This makes the wave appear to have a shorter wavelength. The observer is "running to intercept" the oncoming wave and the next crest or trough will "arrive sooner" because of the relative motion. This gives the effect of a change of frequency of the wave, and it makes it appear higher in frequency (with an accompanying shorter wavelength).

If there is no change in distance between the source and the observer, the wave has a given wavelength. When a crest of the wave arrives at the observer's position, it takes "x" amount of time for the next crest to arrive. That's the period of the wave, or the time it takes for one complete cycle of the wave to occur. If the source and/or observer are/is moving relative to one another and the distance is closing, the "next crest" will "arrive sooner" and the period of the wave is effectively reduced. A shorter period of a wave equates to a higher frequency and a shorter wavelength. As the distance between the observer and the source opens, the opposite effect can be seen. Doppler effect isn't too tough to get a handle on if you work with it and think it through.

If you've ever stood beside a roadway (or railroad track) with a vehicle (or train) coming toward you at speed, it has a given pitch (frequency). As it passes and moves away, the pitch (frequency) goes down. Simple and easy to observe. In astronomy, we note that the colors of stars in very distant galaxies are "wrong" as we observe them, but by "shifting the frequency" to increase it, they take on their "correct" colors. (*We know the "correct" colors due to the obvious pattern of spectral lines which the elements in a star have. The distant galaxies are moving away from us, and the light they emit is lower in frequency as we observe it than it would be if we were not moving apart. That light has been shifted toward the lower end of the optical spectrum, which is toward the red end. This is red shift, or the so-called redshift (one word) you hear about in astrophysics.

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When pitch rises as sound approackes then drops as the source passes by example: sirens

Answer 2

The Doppler effect is the apparent change in the frequency of a wave because of relative motion between the observer and the source. Let's look more closely.

Given a source of a wave and an observer a fixed distance from the source, the wave from the source will arrive at the observer crest after crest after crest. And there will be a fixed time between each crest. This is the period of the wave, or the time it takes for one complete cycle of the wave to occur. (The frequency of a wave is one over the period, and the period of a wave is one over the frequency.) In this scenario, crests will arrive "on schedule" according to the period of the wave. And the frequency of the wave will be observed to be the same as the frequency of the wave generated by the source. Now let's add some relative motion.

If the distance between the source and observer is decreasing, then the observer will be seen to be moving toward the source. And as for the wave, the "next crest" will arrive a bit "sooner" because the observer is "moving to meet" that next crest. The time until the next crest arrives will be shorter for the observer under these circumstances because of the relative motion. The observed wave now has a shorter period, at least according to the observer. That means the frequency of the observed wave is higher because the period is shorter. The source still generates the wave at the original frequency, but the observer sees a wave of higher frequency. If the distance between the source and observer is increasing, the opposite is true.

If an observer is watching, say, a Formula 1 race, Doppler effect will change what is heard from the original sound made by the F1 car. If the observer is in the middle of the straightaway, as the cars come at him, the sound will be higher in frequency, or higher in pitch. The pitch will drop as the car goes by, and the pitch will drop even more after it has passed and is retreating. The frequency had gone up as the vehicle closed, had been about "normal" or of a pitch that was the same as was generated as the car passed, and was of a lower pitch as it continued moving away from the observer. Doppler effect has changed the sound of the car for the observer, though the sound the car originally made has not changed. Use the links for more information.

AnswerThe Doppler effect is the term we give to the apparent change in frequency of light or sound waves as the distance between the source and the observer changes. If either the source or the observer of a wave is moving so that the effect is that they are getting farther apart or closer together, the Doppler effect will appear. Let's look more closely.

If the distance between the observer and the source of a wave is decreasing because they are closing on each other, something happens. The wave, which is normally characterized by a given frequency and an associated wavelength, will appear to increase in frequency (and decrease in wavelength). Let's get even closer and break it down a bit to see what happens.

If a wave is arriving at an observer, it has a given wavelength if there is no change in the distance between that observer and the source. But if the distance of separation is decreasing as the crests and troughs of the wave arrive, the observer will be "running to the next peak or trough" of the wave. This makes the wave appear to have a shorter wavelength. The observer is "running to intercept" the oncoming wave and the next crest or trough will "arrive sooner" because of the relative motion. This gives the effect of a change of frequency of the wave, and it makes it appear higher in frequency (with an accompanying shorter wavelength). Let's look at it another way.

If there is no changein distance between the sourceand the observer, the wavehas a given wavelength. When thecrest of the wave arrivesat the observer's position, ittakes "x" amount of time forthe next crest to arrive. That's the period of the wave, or the time it takes for one complete cycle of the wave to occur. If the source and/or observer are/is moving relative to one another and the distance is closing, the "next crest" will "arrive sooner" and the period of the wave is effectively reduced. A shorter period of a wave equates to a higher frequency and a shorter wavelength. As the distance between the observer and the source opens, the opposite effect can be seen. Doppler effect isn't too tough to get a handle on if you work with it and think it through.

If you've ever stood beside a roadway (or railroad track) with a vehicle (or train) coming toward you at speed, it has a given pitch (frequency) to the sound it is making. As it passes and moves away, the pitch (frequency) goes down. Simple and easy to observe.

In astronomy, we note that the colors of stars in very distant galaxies are "wrong" as we observe them, but by "shifting the frequency" to increase it, they take on their "correct" colors. The distant galaxies are moving away from us, and the light they emit is lower in frequency as we observe it than it would be if we were not moving apart. That light has been shifted toward the lower end of the optical spectrum, which is toward the red end. This is red shift, or the so-called redshift (one word) you hear about in astrophysics.

(Strictly speaking this phenomenon is not a Doppler effect. It's more properly called the "cosmological redshift". We think it's caused by the expansion of space itself.)

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Answer 3

(often lowercase) the shift in frequency (Doppler shift) of acoustic or electromagnetic radiation emitted by a source moving relative to an observer as perceived by the observer: the shift is to higher frequencies when the source approaches and to lower frequencies when it recedes.

Answer 4

A Doppler shift is the change in a wave's wavelegnth caused by the motion of the source relative to that of the observer. The Doppler shift can be easily detected in sound by the ear. An example is when a car honks its horn while approaching you. While approaching the tone will be higher than the actual tone. When the car is opposite you the tone will be its actual value. As the car moves away the tone will be lower (see figure 3-18 in text).

Answer 5

Doppler shift is the apparent change in frequency of a signal, as the emitter of the signal moves towards the measurer, or away from him.

Of great assistance to astronomers, as objects moving towards us are blue-shifted, (signal appears higher in frequency), and those moving away are red-shifted (signal appears to have lowered in frequency).

Answer2:

Doppler shift in Astronomy indicates the body emitting light is under centrifugal force or centripetal force, f=mcDel.V= mcv/r cosV. There is quantum doppler shift in atoms caused again by central forces, centripetal or centrifugal.

The astonomical doppler shift indicates the

Divergence force mcDel.V = -mcv/r cosV. The red shift is the balance between the centripetal and centrifugal force mv2/r= mcv/r cosV gives v/c= cosV the red shift!

The Doppler's shift is when, for example, an ambulance with the siren turned on approaches you. You will notice that when the ambulance comes towards you, the pitch of the sound will be higher than when the ambulance is behind you and moving away from you. That is because there is a change of frequency as the ambulance approaches you and moves away from you.

A Doppler shift is when the movement of sound or light appears to change in frequency based upon the observer's relative position to the sound or light. In standard Newtonian physics, this can be observed by standing near a passing train or emergency vehicle. As the train approaches, the frequency of the sound waves of the horn increases; as the train departs, the frequency of the sound waves of the horn decreases. The same thing happens with light over interstellar distances.

A Doppler shift occurs when there is relative movement between a source of a wave such as a sound source or light emitting/reflecting object and a sensor of the wave such as your ears or eyes.

The motion changes the frequency of the observed wave; this is in reference to the the observer's relative position to the sound or light source in motion. In standard Newtonian physics, this can be observed by standing near a passing train or emergency vehicle. As the train approaches, the frequency of the sound waves of the siren increases (the tone goes up; as the ambulance departs, the frequency of the sound waves of the horn decreases. IIIIIEEEEEE-OOOOWWWWW. Teh same can be heard if on the train you listen to the bells of the crossing signal Pling Pling Pling- Plong Plong Plong.

The same thing happens with light from stars and galaxies moving at great speeds towards (blue shift) or away (red shift) from us (the observers).

Answer 6

The Doppler effect is an apparent change in the frequency of a wave (like light or sound) because the source and observer are getting closer or moving apart. Use the link to the related question "What is Doppler effect?" to learn more.

Answer 7

The Doppler effect is present in any type of wave form when there is a difference in the speed of the source and the speed of the observer. In sound waves, it causes changes in pitch, in light waves it causes changes in color.

Answer 8

The "Doppler effect" is the changes in the observed frequencies

(or wavelengths) of waves, such as sound or light waves, caused by the relative motions of the source or the observer.

When an object is moving away the observed wavelength of its light is longer.

This is called a "redshift" because red light has longest wavelength in the visible spectrum.

The Doppler effect may be experienced with sound when a source emitting a constant frequency passes you. A train whistle is the common example given - when the train passes you the note suddenly lowers.

This effect is used a lot in astronomy, for example the 'redshift' which is used to measure the velocity of distant galaxies.

Strictly speaking this is caused by the expansion of space. It's called the "cosmological redshift". However, it's often referred to as a Doppler effect and it has similar results.

The light given out by, say, the calcium atom is believed to be a constant in the universe, and the spectrum of this light is well known.

From a distant galaxy, the spectrum is shifted towards the red.

Edwin Hubble showed that, generally, the further away a galaxy is, the greater its redshift and hence the faster it is receding from us.

This is "Hubble's Law".

So, the redshift gives us an estimate of the galaxy's recessional velocity.

From "Hubble's Law" we can estimate the distance to a galaxy.

From the assumption that near the time of the Big Bang all galaxies were close together, we are able to estimate the age of the Universe.

The same Doppler effect is used by bats to locate and capture their insect prey. And, some moths have evolved an automatic swerve whenever they detect this chirp, thus evading capture!

It also has use in radar speed traps on the highways.

Answer 9

Doppler effect is the apparent change in the frequency due to motion of the source relative to the listener or vice versa . It is used to compute the velocities of stars relative to earth by noting change in wavelength.

Answer 10

It is a change of frequency due to motion.