Doppler effect

src: i.ytimg.com

The Doppler effect (or Doppler shift ) is the change in frequency or wavelength in relation to the observer moving relative to the source of the wave. It's named after Austrian physicist Christian Doppler, who described the phenomenon in 1842.

A common example of Doppler shift is a change in tone audible when a trumpet-sounding vehicle approaches and away from the observer. Compared to the transmitted frequencies, the received frequencies are higher during the approach, identical at the time of passing, and lower during the recession.

The reason for the Doppler effect is that when the source of the wave moves in the direction of the observer, each successive wave peak is emitted from a position closer to the observer than the previous wave. Therefore, each wave takes slightly less time to reach the observer than the previous wave. Therefore, the time between the arrival of successive wave peaks on the observer decreases, causing an increase in frequency. As they travel, the distance between successive wave fronts decreases, so the wave "gathers together". Conversely, if the source of the wave moves away from the observer, each wave is transmitted from a position farther from the observer than the previous wave, so the time of arrival between successive waves increases, reducing the frequency. The distance between successive wave fronts then increases, so the wave "spreading".

For waves propagating in the media, such as sound waves, observer speed and source relative to the medium in which the waves are transmitted. Therefore, the total Doppler effect can be generated from source movement, observer movement, or medium movement. Each of these effects was analyzed separately. For waves that do not require media, such as light or gravity in general relativity, only the relative difference in speed between observer and source needs to be considered.

Video Doppler effect

Histori

Doppler first proposed this effect in 1842 in his treatise " ÃÆ'Ã…" das farbige Licht der Doppelsterne und einiger anderer Gestirne des Himmels "(On the colored light of binary stars and some other stars from the sky). The hypothesis was tested for sound waves by Buys Ballot in 1845. He asserted that the tone of voice is higher than the frequency emitted when the sound source approaches it, and is lower than the frequency emitted when the sound source recedes from it. Hippolyte Fizeau discovered independently the same phenomenon in electromagnetic waves in 1848 (in France, this effect is sometimes called "effet Doppler-Fizeau" but the name was not adopted by the rest of the world because Fizeau's discovery was six years after Doppler's proposal). In England, John Scott Russell made an experimental study of the effects of Doppler (1848).

Maps Doppler effect

General

In classical physics, where the source and receiver velocities relative to the media are lower than the speed of the wave in the media, the relationship between observed frequencies is ${\ displaystyle f}$ and the frequency transmitted ${\ displaystyle f _ {\ text {0}}}$ is provided by:

${\ displaystyle f = \ left ({\ frac {c \ pm v _ {\ text {r}}} {c \ pm v _ {\ text {s}}}} \ right) f_ {0} \,} Â Â$

where

${\ displaystyle c \;}$ is the speed of the wave in the medium;

${\ displaystyle v _ {\ text {r}} \,}$ is the receiver speed relative to the medium; positive if the recipient is moving toward the source (and negatively in the other direction);

${\ displaystyle v _ {\ text {s}} \,}$ is the source speed relative to the medium; positive if the source moves away from the receiver (and negative in the other direction).

The frequency decreases if one moves away from the other.

The above formula assumes that the source is directly close to or away from the observer. If the source approaches the observer at an angle (but still at a constant velocity), the observed frequency that is first heard is higher than the frequency at which the object emits. After that, there is a monotonic decrease in the observed frequency as it gets closer to the observer, through equality when it comes from a direction perpendicular to the relative motion (and transmitted at the nearest approach point, but when the wave is received). , sources and observers will no longer be near them), and monotonic decline continues as receding observers observe. When the observer is very close to the object path, the transition from high to low frequency is very abrupt. When the observer is away from the object path, transition from high frequency to low frequency gradually.

Jika kecepatan ${\ displaystyle v _ {\ text {s}} \,}  ÂÂ$ dan ${\ displaystyle v _ {\ text {r}} \,}  ÂÂ$ kecil dibandingkan dengan kecepatan gelombang, hubungan antara frekuensi yang diamati ${\ displaystyle f}  ÂÂ$ dan frekuensi yang dipancarkan ${\ displaystyle f _ {\ text {0}}}  ÂÂ$ kira-kira

di mana

${\ displaystyle \ Delta f = f-f_ {0} \,}  ÂÂ$

${\ displaystyle \ Delta v = v _ {\ text {r}} - v _ {\ text {s}} \,}  ÂÂ$ adalah kecepatan penerima relatif terhadap sumber: ini positif ketika sumber dan penerima bergerak ke arah satu sama lain.

src: image.shutterstock.com

Analisis

To understand what happened, consider the following analogy. Someone throws one ball every second at a man. Assume that the ball is running at a constant speed. If the thrower is silent, the person will receive one ball every second. However, if the thrower moves in the direction of the man, he will receive the ball more often because the ball will be less spaced. The reverse is true if the thrower moves away from the man. So in fact is the wavelength affected; as a result, the received frequency is also affected. It can also be said that the wave velocity remains constant while the wavelength changes; then the frequency also changes.

Dengan relatif stasioner pengamat terhadap medium, jika sumber bergerak memancarkan gelombang dengan frekuensi aktual ${\ displaystyle f _ {\ text {0}}}  ÂÂ$ (dalam hal ini, panjang gelombang berubah, kecepatan transmisi gelombang tetap konstan ${\ displaystyle {\ text {-}}}  ÂÂ$ perhatikan bahwa kecepatan transmisi dari gelombang tidak bergantung pada kecepatan sumber ), maka pengamat mendeteksi gelombang dengan frekuensi ${\ displaystyle f}  ÂÂ$ diberikan oleh

${\ displaystyle f = \ left ({\ frac {c} {c \ pm v _ {\ text {s}}}} \ right) f_ {0}}  ÂÂ$

Similar analyzes for moving observers and stationary sources (in this case, the wavelength remains constant, but due to movement, the observer rate receives the wave ${\ displaystyle {\ text {-}}}$ and therefore transmission speed of wave [with respect to observer] ${\ displaystyle {\ text {-}}}$ produces the observed frequencies:

_{           f                ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ,                                {\ displaystyle f = \ left {{\ frac {c \ pm v _ {\ text {r}}} {c}} \ right) f_ { 0}}  Â}

Ini dapat digeneralisasikan ke dalam persamaan yang disajikan di bagian sebelumnya.

${\ displaystyle f = \ left ({\ frac {c \ pm v _ {\ text {r}}} {c \ pm v _ {\ text {s}}}} \ right) f_ {0}}  ÂÂ$

The interesting effect is predicted by Lord Rayleigh in his classic book on sound: if the source moves toward the observer at twice the speed of sound, a piece of music emitted by the source will be heard in the correct time and tone, but backwards . The Doppler effect with sound is only audible with moving objects at high speed, because the frequency change of music tones involves speeds of about 40 meters per second, and smaller frequency changes can easily be confused by changes in the sound amplitude of moving issuers. Neil A Downie has shown how the Doppler effect can be made more audible by using an ultrasonic (eg 40 kHz) emitter on a moving object. The observer then uses a heterodyne frequency converter, as used in many bat detectors, to listen to bands of around 40 kHz. In this case, with the bat detector tuned to give the frequency to the stationary emitter of 2,000 Hz, the observer will see a shift of the overall tone frequency, 240 Hz, if the emitter goes at 2 meters per second.

src: i.ytimg.com

Apps

Sirens

The siren on a passing emergency vehicle will start higher than the stationary, sliding down as it passes, and continue lower than its stationary pitch when it is away from the observer. Astronomer John Dobson explains the effect as follows:

"The reason the siren is shifting because it's not about you."

In other words, if the siren approaches the observer directly, the pitch will remain constant, at a higher position than the stationary, until the vehicle hits it, and then jumps directly to the lower field. Because the vehicle passes by the observer, the radial velocity does not remain constant, but instead varies as a corner function between its line of sight and the speed of the siren:

${\ displaystyle v _ {\ text {radial}} = v _ {\ text {s}} \ cdot \ cos {\ theta}}$

di mana ${\ displaystyle \ theta}  ÂÂ$ adalah sudut antara kecepatan gerak objek dan garis pandang dari objek ke pengamat.

Astronomi

The Doppler effect for electromagnetic waves such as light is very useful in astronomy and produces what is called redshift or blueshift. It has been used to measure the speed at which stars and galaxies approach or move away from us; ie their radial velocity. This can be used to detect if it turns out that a single star, in fact, is binary close, to measure the rotational speed of stars and galaxies, or to detect exoplanets. These red and blue changes occur on a very small scale, if an object moves toward the earth, there will be no noticeable difference in visible light

Note that redshift is also used to measure space expansion, but this is not really a Doppler effect. In contrast, redshifting due to space extension is known as cosmological redshift, which can be derived purely from the Robertson-Walker metric under the General Relativity formula. Having said this, it also happens that there are Doppler effects that can be detected on a cosmological scale, which, if misinterpreted as cosmological origin, leads to observations of redshift-space distortion.

The use of the Doppler effect for light in astronomy depends on our knowledge that the star spectrum is not homogeneous. They show an absorption line at a well-defined frequency that correlates with the energy required to generate electrons in various elements from one level to another. The Doppler effect can be recognized in the fact that the absorption channel is not always at the frequency obtained from the spectrum of stationary light sources. Since blue light has a higher frequency than red light, the spectral lines of near-astronomical light sources show a change in the blue color and the light of the astronomical light source at low tide indicates a redshift.

Among the closest stars, the largest radial velocity with respect to the Sun is 308 km/d (BD-15 Â ° 4041, also known as LHS 52, 81.7 light years) and -260 km/d (Woolley 9722, too). known as Wolf 1106 and LHS 64, 78.2 light years). The positive radial velocity means the star is receding from the Sun, the negative approaching.

Radar

The Doppler effect is used in several types of radar, to measure the speed of detected objects. The radar beam is fired into a moving target - ie. automobiles, because police use radar to detect riders who are speeding - as they approach or move away from radar sources. Each successive radar wave must travel further to reach the car, before it is reflected and detected back near the source. Since each wave must move further, the distance between each wave increases, increasing the wavelength. In some situations, the radar beam is fired into the moving car as it approaches, in which case each successive wave runs at a lower distance, reducing the wavelength. In any situation, the calculation of the Doppler effect accurately determines the speed of the car. In addition, the fuze proximity, developed during World War II, relies on Doppler radar to detonate explosives at the correct time, height, distance, etc..

Because the doppler shift affects the incident of the wave at the target and the wave is reflected back to the radar, the frequency change observed by the radar since the target moves at relative velocity are twice the same target emits wave:

$Â\; ÂÂ\; Â\; Â\; ÂÂ\; Â\; Â\; Â\; Â{\displaystyle Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\mathrm{?}Â\; Â\; Â\; Â\; Â\; Â\; Â\; ÂfÂ\; Â\; Â\; Â\; Â\; Â\; Â\; Â=Â\; Â\; Â\; Â\; Â\; Â\; Â\; ÂÂ\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\frac{Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â2Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\mathrm{?}Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; ÂvÂ\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â}{c}Â\; Â\; Â\; Â\; Â\; Â\; Â\; ÂÂ\; Â\; Â\; Â\; Â\; Â\; Â\; Âf_{Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â0Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â}Â\; Â\; Â\; Â\; Â\; Â}Â\; Â\; Â\; ÂAnnotation\; encoding\; =\; "application/x-tex">\; \{\backslash \; displaystyle\; \backslash \; Delta\; f\; =\; \{\backslash \; frac\; \{2\; \backslash \; Delta\; v\}\; \{c\}\}\; f\_\; \{0\}\}\; Â\; Â$ .

Medical

An echocardiogram can, within certain limits, produce an accurate assessment of the direction of blood flow and the velocity of blood and cardiac tissue at any point by using the Doppler effect. One limitation is that ultrasound rays must be parallel to the possible blood flow. Speed ​​measurements allow assessment of heart valve area and function, abnormal communication between the left and right sides of the heart, leakage of blood through the valves (valvular regurgitation), and calculation of cardiac output. Improved contrast ultrasound using microbubble-filled gas contrast media can be used to improve speed or other flow-related medical measurements.

Although "Doppler" has become synonymous with "speed measurement" in medical imaging, in many cases it is not the frequency shift (Doppler shift) of the received signal being measured, but the phase shift ( when the received signal arrives ).

Blood velocity measurements are also used in other fields of medical ultrasonography, such as midwifery ultrasonography and neurology. Measurement of blood velocity velocities in arteries and veins based on the Doppler effect is an effective tool for the diagnosis of vascular problems such as stenosis.

Flow measurements

Instruments such as laser Doppler velocimeter (LDV), and acoustic Doppler velocimeter (ADV) have been developed to measure the velocity in fluid flow. LDV emits light and ADV emits ultrasonic acoustic bursts, and measures the Doppler shift in the reflection wavelength of the moving particles with the flow. Actual flow is calculated as a function of water velocity and phase. This technique allows non-intrusive flow measurements, at high precision and high frequency.

Speed ​​profile measurements

Developed initially for measurement of speed in medical applications (blood flow), Ultrasonic Doppler Velocimetry (UDV) can measure in real time a complete speed profile in virtually any liquid containing particles in suspensions such as dust, gas bubbles, emulsions. The current may be pulsed, oscillating, laminar or turbulent, stationary or temporary. This technique is completely non-invasive.

Satellite Communications

Fast moving satellites can have a Doppler shift of tens of kilohertz relative to the earth station. Speed, so the magnitude of the Doppler effect, changes because of the curvature of the earth. Doppler dynamic compensation, in which the signal frequency is changed several times during transmission, is used so that the satellite receives a constant frequency signal.

Audio

Speaker Leslie, most often associated with and mostly used with the famous Hammond organ, takes advantage of the Doppler effect by using an electric motor to rotate the acoustic horn around the loudspeaker, sending his voice in a circle. This produces the listener's ear in a rapidly fluctuating keyboard tone frequency.

Vibration measurements

Laser Doppler vibrometer (LDV) is a non-contact instrument for measuring vibration. The laser beam of LDV is directed at the surface of the flower, and the amplitude of vibration and frequency is extracted from the Doppler shift from the frequency of the laser beam due to surface movement.

Developmental biology

During the vertebrate embryo segmentation, the gene expression wave sweeps the presomitic mesomerm, the tissue from which the vertebral precursor (somit) is formed. A new somit is formed at the arrival of waves at the anterior end of the mesoderm of presomit. In zebra fish, it has been shown that the shortening of the presomitic mesoderm during segmentation leads to the Doppler effect when the anterior edge of the tissue moves into the waves. This Doppler effect contributes to the segmentation period.

src: www.exploratorium.edu

Inverse Doppler effect

Since 1968 scientists such as Victor Veselago have speculated on the possibility of the Doppler effect being reversed. Experiments claiming to have detected this effect were carried out by Nigel Seddon and Trevor Bearpark in Bristol, England in 2003.

src: i.ytimg.com

See also

• Doppler Differential Effects
• Doppler cooling
• Dopplergraph
• Fades
• Fizeau trial
• Photoacoustic Doppler effect
• Rayleigh fades
• Redshift
• The Doppler Relativistic Effect

src: www.exploratorium.edu

References

src: i.ytimg.com

Further reading

• Doppler, C. (1842). ÃÆ'Ã… "das farbige Licht der Doppelsterne und einiger anderer Gestirne des Himmels (About the colored light of binary stars and some other stars from the sky) . Publisher: Abhandlungen der KÃÆ'¶nigl. BÃÆ'¶hm. Gesellschaft der Wissenschaften (V. Folge, Bd 2, S. 465-482) [Proceedings of the Royal Bohemian Society of Sciences (Part V, Vol 2)]; Prague: 1842 (published 1903). Some sources mention 1843 as the year of publication because in that year the article was published in Proceedings of the Bohemian Society of Sciences. Doppler itself refers to the publication as "Prag 1842 bei Borrosch und AndrÃÆ'Ã… ©", because in 1842 he had a printed initial edition which he distributed separately.
• "Doppler and Doppler effects", E. N. da C. Andrade, Endeavor Vol. XVIII No. 69, January 1959 (published by ICI London). A historical record of Doppler's original paper and subsequent developments.
• Adrian, Eleni (June 24, 1995). "Doppler Effect". NCSA . Retrieved 2008-07-13 .

src: cdn.publishyourarticles.net

External links

• Doppler effect, [ScienceWorld]
• Doppler Shift for Sound and Light in Mathematics
• Flash simulation and Doppler effect sound effects in Scratch (programming language)
• The Doppler Effect and Sonic Booms (D.A. Russell, Kettering University)
• Video Mashup with Doppler Effect video
• Propagation Waves from John de Pillis. An animation that shows that the speed of a moving wave source does not affect the wave velocity.
• EM Wave Animation from John de Pillis. How electromagnetic waves spread through a vacuum
• Doppler Shift Demo - Interactive flash simulation to show Doppler shift.
• An interactive applet in Physics 2000

Source of the article : Wikipedia