Radiant energy: Difference between revisions
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The term "radiant energy" is most commonly used in the fields of [[radiometry]], [[solar energy]], [[heating]] and [[lighting]], but is also sometimes used in other fields (such as [[telecommunications]]). In modern applications involving transmission of power from one location to another, "radiant energy" is sometimes used to refer to the electromagnetic waves ''themselves'', rather than their ''energy'' (a property of the waves). In the past, the term "electro-radiant energy" has also been used.<ref>Examples: {{patent|US|1005338|"Transmitting apparatus"}}, {{patent|US|1018555|"Signaling by electroradiant energy"}}, and {{patent|US|1597901|"Radio apparatus"}}.</ref> |
The term "radiant energy" is most commonly used in the fields of [[radiometry]], [[solar energy]], [[heating]] and [[lighting]], but is also sometimes used in other fields (such as [[telecommunications]]). In modern applications involving transmission of power from one location to another, "radiant energy" is sometimes used to refer to the electromagnetic waves ''themselves'', rather than their ''energy'' (a property of the waves). In the past, the term "electro-radiant energy" has also been used.<ref>Examples: {{patent|US|1005338|"Transmitting apparatus"}}, {{patent|US|1018555|"Signaling by electroradiant energy"}}, and {{patent|US|1597901|"Radio apparatus"}}.</ref> |
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Since the [[first observation of gravitational waves]] in September 2015, the term "radiant energy" is also applicable to [[gravitational radiation]]. In the event that produced the signal, approximately 3 solar masses of matter was converted to 5.3{{e|47}} joules of gravitational-wave energy, as the two black holes spiralled towards each other, reaching a peak emission rate of 3.6{{e|47}} watts when the black holes collided. |
Since the [[first observation of gravitational waves]] in September 2015, the term "radiant energy" is also applicable to [[gravitational radiation]]. In the event that produced the signal, approximately 3 solar masses of matter was converted to 5.3{{e|47}} joules of gravitational-wave energy, as the two black holes spiralled towards each other, reaching a peak emission rate of 3.6{{e|47}} watts when the black holes collided. <ref name="PRL-20160211">{{cite journal |collaboration=LIGO Scientific Collaboration and Virgo Collaboration |last1=Abbott |first1=Benjamin P. |title=Observation of Gravitational Waves from a Binary Black Hole Merger |url=http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.116.061102 |journal=[[Phys. Rev. Lett.]] |volume=116 |issue=6 |pages=061102 |year=2016 |doi=10.1103/PhysRevLett.116.061102 |arxiv=1602.03837 |lay-summary=https://www.ligo.caltech.edu/system/media_files/binaries/301/original/detection-science-summary.pdf}}</ref> |
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<ref name="Properties">{{cite journal |collaboration=LIGO Scientific Collaboration and Virgo Collaboration |last1=Abbott |first1=Benjamin P. |arxiv=1602.03840 |title=Properties of the binary black hole merger GW150914 |date=11 February 2016}}</ref> |
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==Analysis== |
==Analysis== |
Revision as of 05:46, 9 March 2016
![](http://upload.wikimedia.org/wikipedia/commons/thumb/e/e0/Solar_energy.jpg/220px-Solar_energy.jpg)
In radiometry, radiant energy is the energy of electromagnetic and gravitational radiation.[1] The SI unit of radiant energy is the joule (J). The quantity of radiant energy may be calculated by integrating radiant flux (or power) with respect to time. The symbol Qe is often used throughout literature to denote radiant energy ("e" for "energetic", to avoid confusion with photometric quantities). In branches of physics other than radiometry, electromagnetic energy is referred to using E or W. The term is used particularly when electromagnetic radiation is emitted by a source into the surrounding environment. This radiation may be visible or invisible to the human eye.[2][3]
Terminology use and history
The term "radiant energy" is most commonly used in the fields of radiometry, solar energy, heating and lighting, but is also sometimes used in other fields (such as telecommunications). In modern applications involving transmission of power from one location to another, "radiant energy" is sometimes used to refer to the electromagnetic waves themselves, rather than their energy (a property of the waves). In the past, the term "electro-radiant energy" has also been used.[4]
Since the first observation of gravitational waves in September 2015, the term "radiant energy" is also applicable to gravitational radiation. In the event that produced the signal, approximately 3 solar masses of matter was converted to 5.3×1047 joules of gravitational-wave energy, as the two black holes spiralled towards each other, reaching a peak emission rate of 3.6×1047 watts when the black holes collided. [5] [6]
Analysis
![](http://upload.wikimedia.org/wikipedia/commons/thumb/6/68/TrigaReactorCore.jpeg/333px-TrigaReactorCore.jpeg)
Because electromagnetic (EM) radiation can be conceptualized as a stream of photons, radiant energy can be viewed as the energy carried by these photons. Alternatively, EM radiation can be viewed as an electromagnetic wave, which carries energy in its oscillating electric and magnetic fields. These two views are completely equivalent and are reconciled to one another in quantum field theory (see wave-particle duality).
EM radiation can have various frequencies. The bands of frequency present in a given EM signal may be sharply defined, as is seen in atomic spectra, or may be broad, as in blackbody radiation. In the photon picture, the energy carried by each photon is proportional to its frequency. In the wave picture, the energy of a monochromatic wave is proportional to its intensity. This implies that if two EM waves have the same intensity, but different frequencies, the one with the higher frequency "contains" fewer photons, since each photon is more energetic.
When EM waves are absorbed by an object, the energy of the waves is converted to heat (or converted to electricity in case of a photoelectric material). This is a very familiar effect, since sunlight warms surfaces that it irradiates. Often this phenomenon is associated particularly with infrared radiation, but any kind of electromagnetic radiation will warm an object that absorbs it. EM waves can also be reflected or scattered, in which case their energy is redirected or redistributed as well.
Open systems
Radiant energy is one of the mechanisms by which energy can enter or leave an open system.[7][8][9] Such a system can be man-made, such as a solar energy collector, or natural, such as the Earth's atmosphere. In geophysics, most atmospheric gases, including the greenhouse gases, allow the Sun's short-wavelength radiant energy to pass through to the Earth's surface, heating the ground and oceans. The absorbed solar energy is partly re-emitted as longer wavelength radiation (chiefly infrared radiation), some of which is absorbed by the atmospheric greenhouse gases. Radiant energy is produced in the sun as a result of nuclear fusion.[10]
Applications
Radiant energy is used for radiant heating.[11] It can be generated electrically by infrared lamps, or can be absorbed from sunlight and used to heat water. The heat energy is emitted from a warm element (floor, wall, overhead panel) and warms people and other objects in rooms rather than directly heating the air. Because of this, the air temperature may be lower than in a conventionally heated building, even though the room appears just as comfortable.
Various other applications of radiant energy have been devised.[12] These include:
- Treatment and inspection
- Separating and sorting
- Medium of control
- Medium of communication
Many of these applications involve a source of radiant energy and a detector that responds to that radiation and provides a signal representing some characteristic of the radiation. Radiant energy detectors produce responses to incident radiant energy either as an increase or decrease in electric potential or current flow or some other perceivable change, such as exposure of photographic film.
One of the earliest wireless telephones to be based on radiant energy was invented by Nikola Tesla. The device used transmitters and receivers whose resonances were tuned to the same frequency, allowing communication between them. In 1916, he recounted an experiment he had done in 1896.[13] He recalled that "Whenever I received the effects of a transmitter, one of the simplest ways [to detect the wireless transmissions] was to apply a magnetic field to currents generated in a conductor, and when I did so, the low frequency gave audible notes."
SI radiometry units
Quantity | Unit | Dimension | Notes | ||
---|---|---|---|---|---|
Name | Symbol[nb 1] | Name | Symbol | ||
Radiant energy | Qe[nb 2] | joule | J | M⋅L2⋅T−2 | Energy of electromagnetic radiation. |
Radiant energy density | we | joule per cubic metre | J/m3 | M⋅L−1⋅T−2 | Radiant energy per unit volume. |
Radiant flux | Φe[nb 2] | watt | W = J/s | M⋅L2⋅T−3 | Radiant energy emitted, reflected, transmitted or received, per unit time. This is sometimes also called "radiant power", and called luminosity in Astronomy. |
Spectral flux | Φe,ν[nb 3] | watt per hertz | W/Hz | M⋅L2⋅T −2 | Radiant flux per unit frequency or wavelength. The latter is commonly measured in W⋅nm−1. |
Φe,λ[nb 4] | watt per metre | W/m | M⋅L⋅T−3 | ||
Radiant intensity | Ie,Ω[nb 5] | watt per steradian | W/sr | M⋅L2⋅T−3 | Radiant flux emitted, reflected, transmitted or received, per unit solid angle. This is a directional quantity. |
Spectral intensity | Ie,Ω,ν[nb 3] | watt per steradian per hertz | W⋅sr−1⋅Hz−1 | M⋅L2⋅T−2 | Radiant intensity per unit frequency or wavelength. The latter is commonly measured in W⋅sr−1⋅nm−1. This is a directional quantity. |
Ie,Ω,λ[nb 4] | watt per steradian per metre | W⋅sr−1⋅m−1 | M⋅L⋅T−3 | ||
Radiance | Le,Ω[nb 5] | watt per steradian per square metre | W⋅sr−1⋅m−2 | M⋅T−3 | Radiant flux emitted, reflected, transmitted or received by a surface, per unit solid angle per unit projected area. This is a directional quantity. This is sometimes also confusingly called "intensity". |
Spectral radiance Specific intensity |
Le,Ω,ν[nb 3] | watt per steradian per square metre per hertz | W⋅sr−1⋅m−2⋅Hz−1 | M⋅T−2 | Radiance of a surface per unit frequency or wavelength. The latter is commonly measured in W⋅sr−1⋅m−2⋅nm−1. This is a directional quantity. This is sometimes also confusingly called "spectral intensity". |
Le,Ω,λ[nb 4] | watt per steradian per square metre, per metre | W⋅sr−1⋅m−3 | M⋅L−1⋅T−3 | ||
Irradiance Flux density |
Ee[nb 2] | watt per square metre | W/m2 | M⋅T−3 | Radiant flux received by a surface per unit area. This is sometimes also confusingly called "intensity". |
Spectral irradiance Spectral flux density |
Ee,ν[nb 3] | watt per square metre per hertz | W⋅m−2⋅Hz−1 | M⋅T−2 | Irradiance of a surface per unit frequency or wavelength. This is sometimes also confusingly called "spectral intensity". Non-SI units of spectral flux density include jansky (1 Jy = 10−26 W⋅m−2⋅Hz−1) and solar flux unit (1 sfu = 10−22 W⋅m−2⋅Hz−1 = 104 Jy). |
Ee,λ[nb 4] | watt per square metre, per metre | W/m3 | M⋅L−1⋅T−3 | ||
Radiosity | Je[nb 2] | watt per square metre | W/m2 | M⋅T−3 | Radiant flux leaving (emitted, reflected and transmitted by) a surface per unit area. This is sometimes also confusingly called "intensity". |
Spectral radiosity | Je,ν[nb 3] | watt per square metre per hertz | W⋅m−2⋅Hz−1 | M⋅T−2 | Radiosity of a surface per unit frequency or wavelength. The latter is commonly measured in W⋅m−2⋅nm−1. This is sometimes also confusingly called "spectral intensity". |
Je,λ[nb 4] | watt per square metre, per metre | W/m3 | M⋅L−1⋅T−3 | ||
Radiant exitance | Me[nb 2] | watt per square metre | W/m2 | M⋅T−3 | Radiant flux emitted by a surface per unit area. This is the emitted component of radiosity. "Radiant emittance" is an old term for this quantity. This is sometimes also confusingly called "intensity". |
Spectral exitance | Me,ν[nb 3] | watt per square metre per hertz | W⋅m−2⋅Hz−1 | M⋅T−2 | Radiant exitance of a surface per unit frequency or wavelength. The latter is commonly measured in W⋅m−2⋅nm−1. "Spectral emittance" is an old term for this quantity. This is sometimes also confusingly called "spectral intensity". |
Me,λ[nb 4] | watt per square metre, per metre | W/m3 | M⋅L−1⋅T−3 | ||
Radiant exposure | He | joule per square metre | J/m2 | M⋅T−2 | Radiant energy received by a surface per unit area, or equivalently irradiance of a surface integrated over time of irradiation. This is sometimes also called "radiant fluence". |
Spectral exposure | He,ν[nb 3] | joule per square metre per hertz | J⋅m−2⋅Hz−1 | M⋅T−1 | Radiant exposure of a surface per unit frequency or wavelength. The latter is commonly measured in J⋅m−2⋅nm−1. This is sometimes also called "spectral fluence". |
He,λ[nb 4] | joule per square metre, per metre | J/m3 | M⋅L−1⋅T−2 | ||
See also: |
- ^ Standards organizations recommend that radiometric quantities should be denoted with suffix "e" (for "energetic") to avoid confusion with photometric or photon quantities.
- ^ a b c d e Alternative symbols sometimes seen: W or E for radiant energy, P or F for radiant flux, I for irradiance, W for radiant exitance.
- ^ a b c d e f g Spectral quantities given per unit frequency are denoted with suffix "ν" (Greek letter nu, not to be confused with a letter "v", indicating a photometric quantity.)
- ^ a b c d e f g Spectral quantities given per unit wavelength are denoted with suffix "λ".
- ^ a b Directional quantities are denoted with suffix "Ω".
See also
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Notes and references
- ^ "Radiant energy". Federal standard 1037C
- ^ George Frederick Barker, Physics: Advanced Course, page 367
- ^ Hardis, Jonathan E., "Visibility of Radiant Energy". PDF.
- ^ Examples: US 1005338 "Transmitting apparatus", US 1018555 "Signaling by electroradiant energy", and US 1597901 "Radio apparatus".
- ^ Abbott, Benjamin P.; et al. (LIGO Scientific Collaboration and Virgo Collaboration) (2016). "Observation of Gravitational Waves from a Binary Black Hole Merger". Phys. Rev. Lett. 116 (6): 061102. arXiv:1602.03837. doi:10.1103/PhysRevLett.116.061102.
{{cite journal}}
: Unknown parameter|lay-summary=
ignored (help) - ^ Abbott, Benjamin P.; et al. (LIGO Scientific Collaboration and Virgo Collaboration) (11 February 2016). "Properties of the binary black hole merger GW150914". arXiv:1602.03840.
{{cite journal}}
: Cite journal requires|journal=
(help) - ^ Moran, M.J. and Shapiro, H.N., Fundamentals of Engineering Thermodynamics, Chapter 4. "Mass Conservation for an Open System", 5th Edition, John Wiley and Sons. ISBN 0-471-27471-2.
- ^ Robert W. Christopherson, Elemental Geosystems, Fourth Edition. Prentice Hall, 2003. Pages 608. ISBN 0-13-101553-2
- ^ James Grier Miller and Jessie L. Miller, The Earth as a System.
- ^ Energy transformation. assets.cambridge.org. (excerpt)
- ^ US 1317883 "Method of generating radiant energy and projecting same through free air for producing heat"
- ^ Class 250, Radiant Energy, USPTO. March 2006.
- ^ Anderson, Leland I. (editor), Nikola Tesla On His Work With Alternating Currents and Their Application to Wireless Telegraphy, Telephony and Transmission of Power, 2002, ISBN 1-893817-01-6.
- Lang, Kenneth R. (1999). Astrophysical Formulae. Berlin: Springer. ISBN 978-3-540-29692-8.
- Mischler, Georg (2003). "Radiant energy". Lighting Design Knowledgebase. Retrieved 29 Oct 2008.
- Elion, Glenn R. (1979). Electro-Optics Handbook. CRC Press Technology & Industrial Arts. ISBN 0-8247-6879-5.
Further reading
- Caverly, Donald Philip, Primer of Electronics and Radiant Energy. New York, McGraw-Hill, 1952.
- Whittaker, E. T. (Apr 1929). "What is energy?". The Mathematical Gazette. 14 (200). The Mathematical Association: 401–406. doi:10.2307/3606954. JSTOR 3606954.