A radiometer or roentgenometer is a device for measuring the
radiant flux
In radiometry, radiant flux or radiant power is the radiant energy emitted, reflected, transmitted, or received per unit time, and spectral flux or spectral power is the radiant flux per unit frequency or wavelength, depending on whether the Spec ...
(power) of
electromagnetic radiation
In physics, electromagnetic radiation (EMR) consists of waves of the electromagnetic (EM) field, which propagate through space and carry momentum and electromagnetic radiant energy. It includes radio waves, microwaves, infrared, (visible ...
. Generally, a radiometer is an
infrared radiation detector or an
ultraviolet detector.
Microwave radiometers operate in the
microwave
Microwave is a form of electromagnetic radiation with wavelengths ranging from about one meter to one millimeter corresponding to frequency, frequencies between 300 MHz and 300 GHz respectively. Different sources define different fre ...
wavelengths.
While the term ''radiometer'' can refer to any device that measures electromagnetic radiation (e.g. light), the term is often used to refer specifically to a
Crookes radiometer ("light-mill"), a device invented in 1873 in which a rotor (having vanes which are dark on one side, and light on the other) in a partial vacuum spins when exposed to light.
A common belief (one originally held even by Crookes) is that the momentum of the absorbed light on the black faces makes the radiometer operate.
If this were true, however, the radiometer would spin away from the non-black faces, since the photons bouncing off those faces impart more momentum than the photons absorbed on the black faces.
Photons do exert radiation pressure on the faces, but those forces are dwarfed by other effects.
The currently accepted explanation depends on having just the right degree of vacuum, and relates to the transfer of heat rather than the direct effect of photons.
A
Nichols radiometer demonstrates photon pressure. It is much more sensitive than the Crookes radiometer and it operates in a complete vacuum, whereas operation of the Crookes radiometer requires an imperfect vacuum.
The
MEMS radiometer can operate on the principles of Nichols or Crookes and can operate over a wide spectrum of wavelength and particle energy levels.
MEMS Radiometer United States Patent 7,495,199
See also
* Active cavity radiometer
* Bolometer
* Copernicus
Nicolaus Copernicus (; pl, Mikołaj Kopernik; gml, Niklas Koppernigk, german: Nikolaus Kopernikus; 19 February 1473 – 24 May 1543) was a Renaissance polymath, active as a mathematician, astronomer, and Catholic canon, who formula ...
* His Dark Materials
* Net radiometer
* Photon rocket
* Pyranometer A pyranometer is a type of actinometer used for measuring solar irradiance on a planar surface and it is designed to measure the solar radiation flux density (W/m2) from the hemisphere above within a wavelength range 0.3 μm to 3 μm. The name pyran ...
* Radiation pressure
* Radiometry
Radiometry is a set of techniques for measurement, measuring electromagnetic radiation, including visible light. Radiometric techniques in optics characterize the distribution of the radiation's power (physics), power in space, as opposed to phot ...
* Solar sail
Solar sails (also known as light sails and photon sails) are a method of spacecraft propulsion using radiation pressure exerted by sunlight on large mirrors. A number of spaceflight missions to test solar propulsion and navigation have been p ...
* Spectroradiometer
References
External links
*https://www.youtube.com/watch?v=teEhoUB-FQE&list=UUXrJjdDeqLgGjJbP1sMnH8A Short video pertinent to the topic.
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Electromagnetic radiation meters
Radiometry