Pressure of radiation

The pressure of radiation is the Pression exerted on a surface exposed to a electromagnetic Rayonnement. This effect was deduced theoretically by James Maxwell in 1871 and was detected in experiments by Pyotr Lebedev in 1900 then by Ernest Nichols and Gordon Hull in 1901. This pressure is very low but can be measured for example with a Radiomètre of Nichols.

One can show using the theory of the electromagnetism, the quantum Mécanique or the Thermodynamique, by not making no assumption on the nature of the radiation, that the pressure exerted on a surface exposed to a uniform radiation in all the directions is equal to 1/3 of the total energy radiated per unit of volume. For the radiation of a black Corps balances some with the surface exposed, the density of energy, according to the Loi of Stefan-Boltzmann, is worth 4σT⁴/ C ; where σ is the constant of Stefan-Boltzmann, C is the Speed of light and T is the absolute Température radiation. The third of this energy equalizes with: 2,520×10^-15T⁴ Pa × K ⁴. For example, at the boiling point of water (373,15 K), this pressure is worth approximately 5 micropascals, that is to say twenty times less than one billionth of the Atmospheric pressure.

So low pressures are however able to exert significant effects either because they are exerted on very small particles like the Pollen S or of the electron S, or because they are excercent during a very long amount of time, or because the luminosity is very high as with the Laser S of power or by a very high Température (heart of the star S), or even with the suface of most luminous thus counterbalancing gravity (Limite of Eddington). The pressure of radiation plays a big role in the theory of the emission of electrons by the Sun, the comprehension of the operation of the star S, the study of the Comet S (see also the Effet Yarkovsky and the Effet YORP) as well as other processes Astrophysique S.

In the heart of stars, the temperature is very high: the current models predict a temperature of 15 MK inside the Sun, and in the middle of the stars Supergéante S the temperature could exceed 1 GK. As the pressure of radiation increases with the fourth power of the temperature, it becomes significant, even dominating, with these high temperatures. For example, in the Sun, the pressure of radiation is still low (~ 100 mbar) compared to the pressure of gas (~ 250 Gbar) but in heavier stars, therefore hotter, the pressure of radiation becomes the dominant part of the total pressure.

The Photovoile S (including the Statite S) are a possible method of space Propulsion which would use as driving force the pressure of radiation exerted by the Solar wind on a large sail.

---- In Acoustic, the pressure of radiation is the one-way pressure exerted with the interface between two mediums at the time of the passage of a sound wave.

Simple: Radiation presses

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