What is Thermal radiation: Definition and 79 Discussions

Thermal radiation is electromagnetic radiation generated by the thermal motion of particles in matter. All matter with a temperature greater than absolute zero emits thermal radiation. Particle motion results in charge-acceleration or dipole oscillation which produces electromagnetic radiation.
Infrared radiation emitted by animals (detectable with an infrared camera) and cosmic microwave background radiation are examples of thermal radiation.
If a radiation object meets the physical characteristics of a black body in thermodynamic equilibrium, the radiation is called blackbody radiation. Planck's law describes the spectrum of blackbody radiation, which depends solely on the object's temperature. Wien's displacement law determines the most likely frequency of the emitted radiation, and the Stefan–Boltzmann law gives the radiant intensity.Thermal radiation is also one of the fundamental mechanisms of heat transfer.

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  1. D

    Confusion in thermal radiation concepts - infrared, microwave, etc.

    Microwaves heating is often referred to as dielectric heating, but I'm not sure why this seems so special to specify of all the different thermal radiation frequencies. Doesn't infrared heat the dielectric material as well in a similar process? Isn't radiation heat transfer common for a wide...
  2. A

    A doubt regarding the proof of kirchoff's law of thermal radiation

    In the proof that I have studied, there is a Isothermal cavity that behaves as a black body. there is another small opaque body inside the cavity at the same temperature with emissivity e, absorptivity a and area s. now the irradiation on the small body is Eb = σ times T raised to 4. now the...
  3. J

    How to calculate Laws of Thermal Radiation

    1. Star X has a surface temperature of 10,000 K. How much power does it emit per square meter? Enter numbers only. Do not enter units (watt/m2 is assumed) 2. Star X has a surface temperature of 10,000 K. What is the wavelength of the dominate electromagnetic radiation that Star X emits? Enter...
  4. M

    Thermal radiation question. Please help me explain the theory

    Thermal radiation question. Please help me explain the theory! I want to delete this post.
  5. Telemachus

    Why Is Thermal Radiation Usually Negligible in Solids?

    Hi there. Here is the deal. In my lab work, I've done experiments concerning on heat conduction. Now my professor had corrected my inform, and asked me a question for which I have no answer. I consulted for my work the book "heat conduction in solids" by H.S. Carslaw. The book says at the...
  6. S

    Net thermal radiation from an object outside at night

    I am trying to model the cooling of an object (for example, a sheet of glass) placed outside at night. At the moment I am only considering heat loss by radiation. I know that the net radiation from the object will be: Rnet = Robj - Rsky where: Rnet = the net radiation from the object...
  7. L

    Thermal Radiation: What is Nonthermal Radiation?

    I read somewhere on the net that almost 100 percent of radiation in the universe is thermal. What then is nonthermal radiation? Can it be said that blackbody radiation is purely thermal? What about all the radiation that is reflected, diffracted or partly transmitted by bodies, is that...
  8. phinds

    Fundamental question about thermal radiation

    I've always thought that the following was true but posts in another thread lead me to believe I might have a fundamental misunderstanding. The other thread was a different topic and I didn't want to hijack it, so here's my question. What I THOUGHT was true but am not now sure about: an...
  9. M

    Thermal Radiation v Absorption of Light

    A layman with an interest in quantum mechanics here. Just want to check I understand something... Is the phenomenon of electromagnetic waves being emitted by an atom due to it being hot (black body radiation) different to that of such waves being emitted as a result of absorbing light...
  10. B

    Solve Thermal Radiation HW: Find Temperature Inside Insulating Case

    Homework Statement An ipod is left running inside a thin insulating case 2.5mm thick with thermal conductivity of 0.02W/K/m. The case is black and at 25 degrees C and exchanges energy with its surroundings, all of which are at 20 degrees C by radiation alone. What is the temperature inside...
  11. V

    Find the net thermal radiation

    Homework Statement A solid cylinder of radius r1 = 2.5 cm, length h1 = 5.1 cm, emissivity 0.90, and temperature 28°C is suspended in an environment of temperature 46°C. (a) What is the cylinder's net thermal radiation transfer rate P1? (b) If the cylinder is stretched until its radius is r2...
  12. R

    Thermal radiation from the sun

    We know that heat is transferred from the sun to the Earth via electromagnetic radiation, right? Since no other form of heat transfer can occur in a vacuum that must be the case. We also know (?) that electromagnetic radiation does not dissipate over distance (could be wrong here). If that is...
  13. S

    Thermal radiation experiment, question

    Hiya, I'm doing an experiment to see how thermal radiation affects the temperature of water. I have a container with water inside, which is heated up with a piece of led that rests on the surface of the water. It conducts heat 'sinusoidally', not sure how to describe it. There are seven sensors...
  14. H

    Thermal radiation transfer rate

    See attached pic => <= r=2.2 h=4.9 T= 37 Celsius Ten= 65 Celsius emissivity= 0.81 For the surface area I used: A= 2 pie r^2 + 2 pie r h I converted both r and h into meter For the thermal radiation transfer I used the following equation P= Stefan-boltzmann constant X emessivity X surface...
  15. S

    Thermal Radiation & 'Black Radiation': Explained

    what is 'black radiation' ? or specifically, the meaning of the phrase "radiation in equilibrium with matter"...in the context of thermal radiation. clueless here :'(
  16. A

    Thermal Radiation Energy transfer

    I have a general question regarding Radiation. If the net Thermal Radiation is understood to be : Pnet = Pabs - Prad= σϵA(Tenv^4 - T^4) . How is it that Pnet is negative if the environmental temp is higher than the temp of the object?
  17. T

    Thermal Radiation Homework: Ranking Objects of Same Material

    Homework Statement Consider the following three solid object all made of the same material; 1) Cube of edge length r 2) Sphere of radius r 3) Hemisphere of radius r All object are maintained at a temperature 350K in an envorinment at temperature 300K. Rank the objects according to the...
  18. S

    Thermal Radiation and Heat Engines

    Hey all, This is a simple question: Lets say we have a solid hot-body in outer-space that's emitting thermal radiation. Assuming that it doesn't sublimate, will it simply radiate black-body radiation until it reaches absolute zero? This doesn't sound right. Thanks
  19. L

    In what direction is thermal radiation emitted?

    It is well known that thermal vibrations of molecules produce thermal radiation or photons (infrared and visible): but in what directions? I can understand in a gas or liquid the molecules will be rotating in all directions somewhat uniformly and, thus, photon emission will be uniform in all...
  20. N

    Thermal radiation during black hole collapse

    My question is, when a compact star collapses to form a black hole, how does it manage to dispose of the heat necessary to make this transition? Naively, it would seem that the object can never cool itself fast enough due to increasing gravitational redshift of its thermal radiation. Each...
  21. C

    A question on thermal radiation

    It is common knowledge that black colored surface absorbs light and heat the best. Then it seems to me the next logical leap would to think that black colored surfaces would radiate heat most efficiently. If my assumption is correct, then why do most heating devices, such as oil heater or...
  22. S

    Deriving Average Energy of an Oscillator: Thermal Radiation

    The question: In 1900, Planck used an abstract model consisting of harmonic oscillators with various frequency. Derive an average energy \bar{\epsilon} of a single oscillator where the oscillators of frequency f can only take on discrete energies \epsilon_{n} = nhf, n=0, 1, 2, ... and the...
  23. R

    Thermal Radiation from a Liquid or Gas

    Hello, I've been trying to find out how to calculate heat loss from a gas or liquid vs. temp. My understanding is that this is not a simple blackbody problem for a variety of reasons... guess it's more a gray-body problem. Have not been successful at finding papers or texts which deal with...
  24. S

    Thermal Radiation of MARS problemo

    Homework Statement the thermal radiation of mars Homework Equations i understand Earth radiates at 237W/m^2 into space but i can't find out how much Mars radiates, i know it has an average temp of -55 degrees C so i know its going to be a lot less but i don't know how much. i need this...
  25. G

    What Equations Calculate Thermal Radiation and Wavelength Peak Intensity?

    Homework Statement Consider a 5.50×10 (to the 4th power) object that emits thermal radiation. Homework Equations How much power does it emit per square meter? W What is its wavelength of peak intensity? nm The Attempt at a Solution i am looking for the equations to calculate...
  26. N

    Does Copper's Lack of Dipole Movement Increase Thermal Radiation in Calorimetry?

    I have a question. Assuming I have oil at 80 degrees in a copper calorimetry cup , will the heat loss by thermal radiation be very high and will it affect my values? I am thinking that it would not and that it would be negligible. But i do not know why. I heard somewhere that it would be...
  27. C

    Equilibrium Temperature of a Spherical Black Body Satellite

    b) Real satellites are complicated objects (see photo above). To simplify the problem, suppose the satellite is a spherical black body with a 0.3 m radius. Suppose the satellite's electronics generated 3900 Watts. What would be the equilibrium temperature, Teq, of the satellite? Okeedoke, so...
  28. S

    Heat capacity of thermal radiation

    we need to show that the heat capacity of thermal radiation at constant pressure is infinity. I have an argument, but am not sure if it works. we know that Cp = dQ/dT at constant p, but we also know that p is a function of T only, and therefore that T is a function of P only, therefore if...
  29. Hydr0matic

    Unraveling the mysteries of thermal radiation within quantum mechanics

    The quanta first appeared in modern physics when investigating the nature of thermal radiation, or blackbody radiation. In a sense, it was the beginning of QM. Yet, even though I've read a lot about both BB radiation and quantum theory, I can't really tell you exactly how BB radiation fit into...
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