Radiation pressure

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Radiation pressure is the pressure applied to any surface because of the momentum exchange between the object and the electromagnetic field. This includes the momentum of light or electromagnetic radiation of any wavelengths absorbed, reflected, or emitted (eg black body radiation) by matter at any scale (from macroscopic objects to dust particles to gas molecules).

The forces generated by the radiation pressure are generally too small to be noticed in everyday situations; However, they are important in some physical processes. It mainly includes objects in space where it is usually the main force acting on objects other than gravity, and where the net effect of small forces can have large cumulative effects over long periods of time. For example, whether the effect of solar radiation pressure on a spacecraft from a Viking program has been ignored, the spacecraft will miss the orbit of Mars about 15,000 kilometers. The radiation pressure of starlight is very important in a number of astrophysical processes as well. The importance of radiation pressure increases rapidly at very high temperatures, and can sometimes dwarf the ordinary gas pressure, for example in the interior of stars and thermonuclear weapons.

Radiation pressures are equally accountable by considering the momentum of classical electromagnetic fields or in the case of photons, particles of light. The interaction of electromagnetic waves or photons with matter can involve the exchange of momentum. Because of the law of conservation of momentum, any change in the total momentum of a wave or photon must involve a similar and opposite change in the momentum of the interacted matter (Newton's 3rd law of motion), as illustrated in its accompaniment. images for light cases that are reflected perfectly by the surface. This momentum displacement is a general explanation for what we call radiation pressure.

Video Radiation pressure

Discovery

Johannes Kepler proposed the concept of radiation pressure back in 1619 to explain the observation that the comet's tail always pointed away from the Sun.

The claim that light, as electromagnetic radiation, possessed momentum and thus exerted pressure on whatever surface was exposed published by James Clerk Maxwell in 1862, and was proved experimentally by Russian physicist Pyotr Lebedev in 1900 and by Ernest Fox Nichols and Gordon Ferrie Hull in 1901. The pressure is very weak, but it can be detected by letting the radiation fall onto the fine chunks of the reflective metal in the Nichols radiometer (this should not be confused with the Crookes radiometer, whose particular motion is not caused by radiation pressure but by affecting the gas molecule).

Maps Radiation pressure

Theory

Radiation pressure can be seen as a consequence of momentum conservation considering the momentum associated with electromagnetic radiation. The momentum can also be well calculated based on electromagnetic theory or from a combination of photon flow moments, giving identical results as shown below.

Radiation pressure from electromagnetic wave momentum

According to Maxwell's theory of electromagnetism, electromagnetic waves carry momentum, which is transferred to the opaque surface it produces.

Energi fluks (irradiance) dari gelombang pesawat dihitung menggunakan vektor Poynting ${\ displaystyle \ mathbf {S} = \ mathbf {E} \ times \ mathbf {H}} Â Â$ , yang besarnya kami nyatakan dengan S. S dibagi dengan kecepata cahaya adalah densitas momentum linier per satuan luas (tekanan) dari medan elektromagnetik. Tekanan itu dialami sebagai tekanan radiasi di permukaan:

${\ displaystyle P _ {text {incident}} = {\ frac {\ langle S \ rangle} {c}} = {\ frac {I_ { f}} {c}}} Â Â$

di mana ${\ displaystyle P} Â$ adalah tekanan (biasanya dalam Pascal), ${\ displaystyle I_ {f}} Â$ adalah radiasi irradiance (biasanya dalam W/m ² ) dan ${\ displaystyle c} Â Â$ adalah kecepat cahaya dalam ruang hampa.

Jika permukaan planar pada suatu sudut? ke gelombang insiden, intensitas di permukaan akan dikurangi secara geometrik oleh kosinus dari sudut itu dan komponen gaya radiasi terhadap permukaan juga akan dikurangi oleh kosinus, sehingga menghasilkan tekanan:

${\ displaystyle P _ {\ text {incident}} = {\ frac {I_ {f}} {c}} \ cos ^ {2} \ alpha}  ÂÂ$

The momentum of the incoming waves is in the same direction of the wave. But only components of the normal momentum to the surface contribute to the pressure on the surface, as given above. Components of forces that are tangent to the surface are not called pressure.

Radiation pressure from reflections

The above treatment for a wave of incoming waves for the radiation pressure experienced by the black body (completely absorbing). If the wave is reflected specifically, then the recoil because the reflected wave will further contribute to the radiation pressure. In the case of a perfect reflector, this pressure will be identical to the pressure caused by the incident wave:

$Â\; Â{\displaystyle Â\; Â\; Â\; Â\; Â\; Â\; Â}$ _{    Â   P                        emitted                          =                        Â    Â         I                             f        ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ,          Â      ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂï <½                                {\ displaystyle P _ {\ text {emitted}} = {\ frac {I_ {f}} {c}}}  Â}

deny demographic menggandakan tekanan radiasi bersih di permukaan:

${\ displaystyle P _ {text {net}} = P _ {\ text {incident}} P _ {text {emitted}} = 2 { \ frac {I_ {f}} {c}}} Â Â$

For partial reflective surfaces, the second term must be multiplied by reflectivity, so that the increase is less than twice that. For diffuse reflective surfaces, the details of reflection and geometry must be taken into account, again resulting in a rise in net radiation pressure less than twice that.

Radiation pressure by emission

Sama seperti gelombang yang dipantulkan dari sebuah tubuh berkontribusi terhadap tekanan radiasi bersih yang dialami, sebuah tubuh yang memancarkan radiasi sendiri (bukan dipantulkan) memperoleh tekanan radiasi lagi yang diberikan oleh radiasi pancaran itu dalam arah normal ke permukaan Saya _e :

${\ displaystyle P _ {\ text {emitted}} = {\ frac {I_ {e}} {c}}}  ÂÂ$

Emissions may come from black body radiation or other radiation mechanisms. Because all materials emit black body radiation (unless they are completely reflective or zero zero), these sources for radiation pressure are everywhere but usually very small. However, because black body radiation increases rapidly with temperature (according to the strength of the four temperatures as provided by Stefan-Boltzmann's law), radiation pressures due to the temperature of very hot objects (or due to the black body radiation coming in from the same heat of the environment) can become very significant. This becomes important in the interior of stars that are in the millions of degrees.

Radiation pressure in photon form

Radiasi elektromagnetik dapat dilihat dalam hal partikel bukan gelombang; partikel-partikel ini dikenal sebagai photo. Photon tidak memiliki massa-istirahat, namun foton tidak pernah beristirahat (mereka bergerak dengan kecephaha cahaya) dan memperoleh momentum tetap yang diberikan oleh:

${\ displaystyle p = {\ dfrac {h} {\ lambda}} = {\ frac {E_ {p}} {c}},} Â Â$

Did it take p adalah momentum, h adalah constant Planck ,? adalah panjang gelombang, dan c adalah kecepatan cahaya dalam ruang hampa. Dan E _p adalah energi dari satu foto yang diberikan oleh:

${\ displaystyle E_ {p} = h \ nu = {\ frac {hc} {\ lambda}}} Â Â$

The radiation pressure can again be seen as the momentum transfer of each photon to the opaque surface, plus momentum because the (possibly) photon rekoil to surface (partially) reflects. Since the irradiated radiation wave I _f above the area A has the power I _f A , this implies a substantial flux of photons per second per unit area of ​​striking surface. Combining this with the above expression for single photon momentum, produces the same relationship between the radiation and radiation pressure described above using classical electromagnetic. And again, the reflected or emitted photons will contribute to the identical radiation pressure of the net.

Compression in uniform radiation field

The body surface in thermal equilibrium with its surroundings at temperature T , will be surrounded by a uniform radiation field described by Planck's black body radiation law, and will experience compression pressures due to the overwrite radiation, its reflections, and its own black body emission. It can be shown that the resulting pressure is equal to one-third of the total radiant energy per unit volume in the surrounding space.

Secara kuantitatif, ini dapat dinyatakan sebagai

${\ displaystyle P _ {text {compress}} = {\ frac {u} {3}} = {\ frac {4 \ sigma} {3c }} T4} Â Â$

di mana ${\ displaystyle \ sigma}  ÂÂ$ adalah konstanta Stefan-Boltzmann. ${\ displaystyle u}  ÂÂ$ adalah kepadatan radiasi per satuan volume (biasanya dalam JÂ · m ^-3 ) yang dihasilkan dari suhu T (dalam kelvin) dengan asumsi kesetimbangan termal.

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Tekanan radiasi matahari

The pressure of solar radiation is caused by solar radiation at closer distances, so especially in the solar system. While acting on all objects, the net effect is generally larger on smaller objects because they have a greater surface area to mass ratio. All spacecraft are subjected to such pressure except when they are behind the shadow of the earth.

The solar radiation pressure on objects near the Earth can be calculated using solar radiation at 1 AU, known as the solar constants, whose values ​​are set at 1361 W/m ² as the year 2011.

All stars have a spectral energy distribution that depends on their surface temperature. The distribution is roughly the same as the black body radiation. This distribution should be taken into account when calculating radiation pressure or identifying reflector material to optimize the sun screen for example.

Absorption and reflection pressures

Tekanan radiasi matahari por jarak bumi dari matahari, dapat dihitung dengan membagi konstanta matahari W (atas) oleh kecepata cahaya c. Untuk lembaran penyerap yang menghadap matahari, ini hanyalah:

${\ displaystyle P = {\ frac {W} {c}} \ kira-kira 4.5 \ cdot 10 ^ {- 6} {\ textsf { Pa}} = 4.5 \ mu {\ SMSf {Pa}}} Â Â$

Hasil ini dalam Pascal unit S.I., setara dengan N/m ² (Newton per meter persegi). Untuk lembaran pada suatu sudut? that matahari, area efektif A dari lembaran dikurangi oleh faktor geometri yang menghasilkan gaya dalam arah sinar matahari dari:

${\ displaystyle F = {\ frac {W} {c}} (A \ cos \ alpha)} Â Â$

Untuk menemukan komponen gaya ini normal ke permukaan, faktor kosinus lain harus diterapkan sehingga dekanan P pada permukaan:

${\ displaystyle P = {\ frac {F} {A}} = {\ frac {W} {c}} \ cos ^ {2} \ alpha }$

Note, however, that to take into account the net effect of solar radiation on a spacecraft for example, one would need to consider the total power (in the direction away from the sun) provided by its predecessor. equations, not just normal components to the surface that we identify as "pressure".

Permanent matahari didefinisikan untuk radiasi matahari di kejauhan that bumi, juga dikenal sebagai satu satuan astronomi (AU). Akibatnya, by each R unit astronomi ( R sehingga tidak berdimensi), menerapkan hukum kuadrat terbalik, kita akan menemukan:

${\ displaystyle P = {\ frac {W} {cR2}} \ cos2}} Â Â$

Akhirnya, mengingat tidak menyerap tetapi permukaan yang menterminkan sempurna, tekanannya second kali lipat karena gelombang pantulan, sehingga:

${\ displaystyle P = 2 {\ frac {W} {cR2}} \ cos2}} Â Â$

Note that unlike the absorbent case, the resulting force on the reflecting body is given precisely by this pressure that works normally to the surface, with tangential forces of the incident and reflecting mutually canceling waves. In practice, the material does not fully reflect or completely absorb, so the resulting force will be the weighted average of the forces calculated using this formula.

Radiation radiation perturbation

The pressure of solar radiation is the source of orbital disorders. This significantly affects the orbits and trajectories of small bodies including all spacecraft.

The pressure of solar radiation affects the body in many parts of the Solar System. Small bodies are more affected than large because of their lower mass relative to their surface area. The spacecraft is affected along with the natural body (comet, asteroid, dust grain, gas molecule).

Radiation pressures produce strength and torque in the body that can change their translational and rotational motions. Translation changes affect the body's orbit. Rotation rate may increase or decrease. Loosely aggregated bodies can break below the high rotation level. Dust granules can leave the Solar System or a spiral to the Sun.

The whole body usually consists of various surfaces that have different orientations on the body. The facet may be flat or curved. They will have different areas. They may have different optical properties from other aspects.

At certain times, some aspects will be exposed to the Sun and some will be in the shadows. Any surface affected by the Sun will reflect, absorb, and emit radiation. Aspects in the shadows will radiate radiation. The sum of pressures in all aspects will determine the total force and torque of the body. This can be calculated using the equation in the previous section.

The Yarkovsky effect affects the translation of the small body. This results from the face leaving the sun's exposure to be at a higher temperature than the face approaching the sun's exposure. Radiation emitted from a warmer face will be stronger than the opposite face, resulting in a total force on the body that will affect its movement.

The YORP effect is a collection of effects that develop on the initial concept of the Yarkovsky effect, but of a similar nature. It affects the spin properties of the body.

The Poynting-Robertson effect applies to grain size particles. From the perspective of the dust grains surrounding the Sun, the radiation of the Sun seems to come from a slightly forward direction (light aberration). Therefore, the absorption of this radiation leads to forces with components against the direction of movement. (A small aberration angle because the radiation moves at the speed of light while the dust grains move much more slowly than that.) The result is a gradual spiral of dust grains into the Sun. Over a long period of time, this effect clears up a lot of dust in the Solar System.

Though rather small compared to other forces, the force of radiation pressure is not negotiable. Over a long period of time, the net effect of the force is enormous. Such weak stresses can produce marked effects on small particles such as gas ions and electrons, and are essential in the theory of electron emission from the Sun, comet material, and so on.

Since the ratio of surface area to volume (and thus mass) increases with decreasing particle size, dusty particles (micrometer-sized) are susceptible to radiation pressure even in the outer solar system. For example, the evolution of the outer rings of Saturn is significantly influenced by the radiation pressure.

As a result of the light pressure, Einstein predicted in the year 1909 "radiation friction" that would oppose the movement of matter. He writes, "The radiation will apply pressure on both sides of the plate.The pressure pressure applied to both sides is the same if the plate is resting, but if it is moving, more radiation will be reflected on the front surface during movement (front surface) than in the backward force The backward acting force of pressure applied to the front surface is thus greater than the force of pressure acting on the back.Therefore, as a result of the two forces, there remains a force against plate motion and which increases with the speed of the plates. will call this 'friction of radiation' briefly. "

Solar display

Solar sailing, an experimental method of spacecraft propulsion, uses radiation pressure from the Sun as a motive force. The idea of ​​interplanetary travel by light is mentioned by Jules Verne in From Earth to the Moon .

A screen reflects about 90% of the radiation that occurs. 10% absorbed radiated from both surfaces, with the proportion emitted from the non-lit surface depending on the thermal conductivity of the screen. A sail has curvature, surface irregularities, and other minor factors that affect its performance.

The Japan Space Exploration Agency (JAXA) has managed to unfurl a sun screen in space that has managed to drive its load with the IKAROS project.

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Cosmic effect of radiation pressure

Radiation pressures have a profound effect on the development of the cosmos, from the birth of the universe to the formation of sustainable stars and the formation of clouds of dust and gas at various scales.

The early universe

The photon era is a phase when the energy of the universe is dominated by photons, between 10 seconds and 380,000 years after the Big Bang.

Galactic formation and evolution

The process of galactic formation and evolution began in the early history of the cosmos. Early universe observations strongly suggest that objects grow from the bottom up (ie, smaller objects join to form larger ones). Since stars are formed and become sources of electromagnetic radiation, radiation pressure from stars becomes a factor in the remaining material state of the remaining state.

Dust and gas cloud

The gravitational compression of dust and gas clouds is strongly influenced by radiation pressures, especially when condensation causes the birth of stars. The larger young stars formed inside the compressed cloud radiate intense levels of radiation that shift clouds, causing either dispersion or condensation in nearby areas, affecting birth rates in nearby areas.

Star cluster

Stars mainly form in large clouds of dust and gas, giving rise to star clusters. The radiation pressure from the member stars ultimately disperses the cloud, which can have profound effects on the evolution of clusters.

Many open clusters are inherently unstable, with a mass sufficiently small that the velocity out of the system is lower than the average speed of the constituent star. These groups will rapidly spread over several million years. In many cases, stripping of the gas from which the group formed by the radiation pressure of the hot young star reduces the mass of the clusters sufficiently to allow rapid spread.

Star formation

The formation of stars is a process in which the solid areas in a molecular cloud in the interstellar space collapse to form stars. As a branch of astronomy, star formation involves the study of interstellar medium and giant molecular cloud (GMC) as a precursor for star formation, and the study of protostars and star objects as their immediate products. The theory of star formation, as well as accounting for the formation of a single star, must also take into account binary star stats and initial mass functions.

Star planetary system

Planetary systems are generally believed to form as part of the same process that results in star formation. The protoplanetary disk is formed by the gravitational collapse of the molecular cloud, called the solar nebula, and then evolved into a planetary system by collision and gravitational capture. Radiation pressure can clean the area around the star. As the formation process continues, radiation pressure continues to play a role in influencing the distribution of matter. In particular, dust and grains can rotate into stars or out of the star system under the action of radiation pressure.

Interior star

In the interior of the star the temperature is very high. The star model predicts a temperature of 15 MK in the center of the Sun, and at the core of a temperature supergiant star may exceed 1 GK. Because the radiation pressure is scaled as the fourth power of temperature, it becomes important at this high temperature. In the Sun, radiation pressure is still quite small when compared to gas pressure. In the heaviest non-degenerating star, radiation pressure is the dominant pressure component.

Comet

The pressure of solar radiation greatly affects the comet. Solar heating causes the gas to escape from the comet nucleus, which also carries dust grains. The pressure of radiation and the solar wind then pushes the dust and gas away from the Sun's direction. The gas forms a generally straight tail, while the slower moving dust particles create a wider curved tail.

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Application laser radiation pressure

Laser cooling is applied to cooling materials very close to absolute zero. Atoms moving toward a laser light source feel the doppler effect that is tuned to the absorption frequency of the target element. The radiation pressure at the atom slows down in certain directions until the Doppler effect moves out of the element's frequency range, causing an overall cooling effect.

Large lasers operating in space have been suggested as a means of encouraging sailing crafts in light-powered propulsion.

The reflection of the laser pulses from the elastic solid surface gives rise to various types of elastic waves that propagate within the solid. The weakest wave is generally the wave generated by the radiation pressure that works during the reflection of light. More recently, elastic waves induced by light pressure are observed in ultrasonic-reflectivity dielectric mirrors. This wave is the most basic fingerprint of light matter interaction on a macroscopic scale.

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See also

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References

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Further reading

• Demir, Dilek, "Demonstration of radiation pressure on the table" , 2011, Diplomathesis, E-Theses univie (http://othes.univie.ac.at/16381/)
• R. Shankar, "Principles of Quantum Mechanics", 2nd ed. [1]

Source of the article : Wikipedia