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25cm with Lights Black and White World Globes Hd Students In Chinese and English Geographic Globesfor Office Home Decoration

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Radiometers are now commonly sold worldwide as a novelty ornament; needing no batteries, but only light to get the vanes to turn. They come in various forms, such as the one pictured, and are often used in science museums to illustrate "radiation pressure" – a scientific principle that they do not in fact demonstrate. Worrall, J. (1982). "The pressure of light: The strange case of the vacillating 'crucial experiment' ". Studies in History and Philosophy of Science. 13 (2): 133–171. Bibcode: 1982SHPSA..13..133W. doi: 10.1016/0039-3681(82)90023-1. The effect begins to be observed at partial vacuum pressures of several hundred pascals (or several torrs), reaches a peak at around 1 pascal (0.0075 torrs) and has disappeared by the time the vacuum reaches 1 ×10 −4 pascals (7.5 ×10 −7 torrs) ( see explanations note 1). At these very high vacuums the effect of photon radiation pressure on the vanes can be observed in very sensitive apparatus (see Nichols radiometer), but this is insufficient to cause rotation. Wolfe, David; Larraza, Andres (2016). Alejandro Garcia. "A Horizontal Vane Radiometer: Experiment, Theory, and Simulation". Physics of Fluids. 28 (3): 037103. arXiv: 1512.02590. Bibcode: 2016PhFl...28c7103W. doi: 10.1063/1.4943543. S2CID 119235032.

The currently accepted theory was formulated by Osborne Reynolds, who theorized that thermal transpiration was the cause of the motion. [11] Reynolds found that if a porous plate is kept hotter on one side than the other, the interactions between gas molecules and the plates are such that gas will flow through from the cooler to the hotter side. The vanes of a typical Crookes radiometer are not porous, but the space past their edges behaves like the pores in Reynolds's plate. As gas moves from the cooler to the hotter side, the pressure on the hotter side increases. When the plate is fixed, the pressure on the hotter side increases until the ratio of pressures between the sides equals the square root of the ratio of absolute temperatures. Because the plates in a radiometer are not fixed, the pressure difference from cooler to hotter side causes the vane to move. The cooler (white) side moves forward, pushed by the higher pressure behind it. From a molecular point of view, the vane moves due to the tangential force of the rarefied gas colliding differently with the edges of the vane between the hot and cold sides. [3] The air pressure inside the bulb needs to strike a balance between too low and too high. A strong vacuum inside the bulb does not permit motion, because there are not enough air molecules to cause the air currents that propel the vanes and transfer heat to the outside before both sides of each vane reach thermal equilibrium by heat conduction through the vane material. High inside pressure inhibits motion because the temperature differences are not enough to push the vanes through the higher concentration of air: there is too much air resistance for "eddy currents" to occur, and any slight air movement caused by the temperature difference is damped by the higher pressure before the currents can "wrap around" to the other side. [6] Movement with radiation [ edit ]Another incorrect theory was that the heat on the dark side was causing the material to outgas, which pushed the radiometer around. This was later effectively disproved by both Schuster's experiments [9] (1876) and Lebedev's (1901) [8] Partially correct theory [ edit ]

Han, Li-Hsin; Shaomin Wu; J. Christopher Condit; Nate J. Kemp; Thomas E. Milner; Marc D. Feldman; Shaochen Chen (2011). "Light-Powered Micromotor: Design, Fabrication, and Mathematical Modeling". Journal of Microelectromechanical Systems. 20 (2): 487–496. doi: 10.1109/JMEMS.2011.2105249. S2CID 11055498. The reason for the rotation was a cause of much scientific debate in the ten years following the invention of the device, [1] [2] but in 1879 the currently accepted explanation for the rotation was published. [3] [4] Today the device is mainly used in physics education as a demonstration of a heat engine run by light energy. Ohio, The University of Akron. "the radiometer using inquiry to teach energy conversions". The University of Akron, Ohio . Retrieved 10 October 2021.

Maxwell, J. Clerk (1 January 1879). "On stresses in rarefied gases arising from inequalities of temperature". Philosophical Transactions of the Royal Society of London. 170: 231–256. doi: 10.1098/rstl.1879.0067. In 2010 researchers at the University of California, Berkeley succeeded in building a nanoscale light mill that works on an entirely different principle to the Crookes radiometer. A gold light mill, only 100 nanometers in diameter, was built and illuminated by laser light that had been tuned. The possibility of doing this had been suggested by the Princeton physicist Richard Beth in 1936. The torque was greatly enhanced by the resonant coupling of the incident light to plasmonic waves in the gold structure. [16] See also [ edit ] Reynolds, Osborne (1 January 1879). "On certain dimensional properties of matter in the gaseous state …". Philosophical Transactions of the Royal Society of London. 170: 727–845. doi: 10.1098/rstl.1879.0078. ; Part 2. Han, Li-Hsin; Shaomin Wu; J. Christopher Condit; Nate J. Kemp; Thomas E. Milner; Marc D. Feldman; Shaochen Chen (2010). "Light-Powered Micromotor Driven by Geometry-Assisted, Asymmetric Photon-heating and Subsequent Gas Convection". Applied Physics Letters. 96 (21): 213509(1–3). Bibcode: 2010ApPhL..96u3509H. doi: 10.1063/1.3431741. Archived from the original on 22 July 2011. US 182172,Crookes, William,"Improvement in Apparatus For Indicating The Intensity of Radiation",published 1876-09-12

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