Efiko de Doppler: Malsamoj inter versioj

'''Efiko de Doppler''' aŭ '''Doppler-efiko''' aŭ '''Doppler-a efiko''', nomita laŭ [[Christian Andreas Doppler]], estas la ŝajna ŝanĝiĝo en frekvenco kaj ondolongo kiun observanto perceptas moviĝante relative al la ondofonto. La efiko Doppler povas rezulti el moviĝado de la observanto, aŭ de la observata ondofonto, aŭ ambaŭ. Ĉe ondoj bezonantaj perilon (ekzemple, sonaj ondoj) por transmoviĝi, oni devas analizi la moviĝojn (de la observanto resp. de la fonto) aparte; ĉe ondoj ne bezonantaj perilon (ekz-e lumaj aŭ la gravito en speciala relativeco, nur la relativan diferencon en rapido oni devas konsideri.

 

Doppler unue proponis la efikon, pri lum-ondoj, en la monografiaĵo (1842) ''Über das farbige Licht der Doppelsterne und einige andere Gestirne des Himmels'' (''Pri la kolora lumo de la binaraj steloj kaj aliaj astroj''). [[Christoph Hendrik Diederik Buys Ballot]] en [[1845]] testis la proponon ĉe son-ondoj, konfirmante ke la tonalto de sono estas observata kiel pli alta dum la fonto alproksimiĝas, ol dum ĝi formoviĝas. [[Hippolyte Fizeau]] sendepende malkovris la saman fenomenon ĉe [[elektromagnetaj ondoj]] en [[1848]], pro kio oni kelkfoje nomas ĝin (precipe en Francio) la "efiko Doppler-Fizeau").

 

Ni havas du objektojn. Unue estas fonto, due estas observanto. Fonto emisias signalon pri frekvenco <math>f_0</math> ( ondlongo <math>\lambda_0</math>) kaj ĝi veturas per rapido <math>v_0</math>.

::<math> s = v _ {rr} T_0 \;.</math>

ondlongon, kiun observas observanto estas:

 

kie:

 

Estas grave kompreni, ke la frekvenco de la sonoj "elmetataj" de la fonto ''ne efektive ŝanĝiĝas.'' <!--It is important to realize that the frequency of the sounds that the source ''emits'' does not actually change. To understand what happens, consider the following analogy. Someone throws one ball every second in a man's direction. Assume that balls travel with constant velocity. If the thrower is stationary, the man will receive one ball every second. However, if the thrower is moving towards the man, he will receive balls more frequently because the balls will be less spaced out. The converse is true if the thrower is moving away from the man. So it is actually the ''wavelength'' which is affected; as a consequence, the perceived frequency is also affected.

 

The first attempt to extend Doppler's analysis to [[light]] waves was soon made by [[Armand-Hippolyte Fizeau|Fizeau]]. In fact, light waves do not require a medium to propagate and the correct understanding of the Doppler effect for light requires the use of the [[Special relativity|Special Theory of Relativity]]. See [[relativistic Doppler effect]]. -->

 

[[Dosiero:Doppler-effect-two-police-cars-diagram.png|thumb|350px|Fiksita mikrofono registras moviĝantajn policajn sirenojn je malsamaj tonaltoj depende de iliaj relativaj direktoj.]]

 

<!-- The [[siren (noisemaker)|siren]] on a passing [[emergency vehicle]] will start out higher than its stationary pitch, slide down as it passes, and continue lower than its stationary pitch as it recedes from the observer. Astronomer [[John Dobson (astronomer)|John Dobson]] explained the effect thus:

:"The reason the siren slides is because it doesn't hit you."

where ''v''_s is the velocity of the object (source of waves) with respect to the medium, and <math>\theta</math> is the angle between the object's forward velocity and the line of sight from the object to the observer. -->

 

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[[Dosiero:Redshift.png|thumb|200px|[[Ruĝeniĝo]] of [[spektra linio|spektraj linioj]] en la optika spektro de supergrapolo de lontanaj galaksioj (dekstre) kompare al la suno (maldekstre).]]

Among the [[List of nearest stars|nearby stars]], the largest radial velocities with respect to the [[Sun]] are +308 km/s ([[BD-15°4041]], also known as LHS 52, 81.7 light-years away) and -260 km/s ([[Woolley 9722]], also known as Wolf 1106 and LHS 64, 78.2 light-years away). Positive radial velocity means the star is receding from the Sun, negative that it is approaching.-->

 

<!-- Another use of the Doppler effect which is found mostly in astronomy, is the estimation of the temperature of a gas which is emitting a [[spectral line]]. Due to the thermal motion of the gas, each emitter can be slightly red or blue shifted, and the net effect is a broadening of the line. This line shape is called a [[Doppler broadening|Doppler profile]] and the width of the line is proportional to the square root of the temperature of the gas, allowing the Doppler-broadened line to be used to measure the temperature of the emitting gas. -->

 

<!-- ''Main article: [[Doppler radar]]''

 

The [[Proximity fuze]] which was developed during [[World War II]] also relies on Doppler radar. -->

 

<!-- An [[echocardiogram]] can within certain limits produce accurate assessment of the direction of blood flow and the velocity of blood and cardiac tissue at any arbitrary point using the doppler effect. One of the limitations is that the [[ultrasound]] beam should be as parallel to the blood flow as possible. Velocity measurements allow assessment of cardiac valve areas and function, any abnormal communications between the left and right side of the heart, any leaking of blood through the valves (valvular regurgitation), and calculation of the [[cardiac output]]. [[Contrast enhanced ultrasound]] using gas-filled microbubble contrast media can be used to improve velocity or other flow-related medical measurements.

 

Velocity measurements of blood flow are also used in other fields of [[medical ultrasonography]], such as [[obstetric ultrasonography]] and [[neurology]]. Velocity measurement of blood flow in arteries and veins based on doppler effect is an effective tool for diagnosis of vascular problems like stenosis. -->

 

<!-- Instruments such as the [[laser Doppler velocimetry|laser Doppler velocimeter]] (LDV), and [[Acoustics|Acoustic]] Doppler Velocimeter (ADV) have been developed to measure [[velocity|velocities]] in a fluid flow. The LDV and ADV emit a light or acoustic beam, and measure the doppler shift in wavelengths of reflections from particles moving with the flow. This technique allows non-intrusive flow measurements, at high precision and high frequency.

-->

 

 

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