What is Black body: Definition and 159 Discussions

A black body or blackbody is an idealized physical body that absorbs all incident electromagnetic radiation, regardless of frequency or angle of incidence. The name "black body" is given because it absorbs all colors of light. A black body also emits black-body radiation. In contrast, a white body is one with a "rough surface that reflects all incident rays completely and uniformly in all directions."A black body in thermal equilibrium (that is, at a constant temperature) emits electromagnetic black-body radiation. The radiation is emitted according to Planck's law, meaning that it has a spectrum that is determined by the temperature alone (see figure at right), not by the body's shape or composition.
An ideal black body in thermal equilibrium has two notable properties:
It is an ideal emitter: at every frequency, it emits as much or more thermal radiative energy as any other body at the same temperature.
It is a diffuse emitter: measured per unit area perpendicular to the direction, the energy is radiated isotropically, independent of direction.An approximate realization of a black surface is a hole in the wall of a large insulated enclosure (an oven, for example). Any light entering the hole is reflected or absorbed at the internal surfaces of the body and is unlikely to re-emerge, making the hole a nearly perfect absorber. When the radiation confined in such an enclosure is in thermal equilibrium, the radiation emitted from the hole will be as great as from any body at that equilibrium temperature.Real materials emit energy at a fraction—called the emissivity—of black-body energy levels. By definition, a black body in thermal equilibrium has an emissivity ε = 1. A source with a lower emissivity, independent of frequency, is often referred to as a gray body.
Constructing black bodies with an emissivity as close to 1 as possible remains a topic of current interest.In astronomy, the radiation from stars and planets is sometimes characterized in terms of an effective temperature, the temperature of a black body that would emit the same total flux of electromagnetic energy.

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  1. B

    Why is Black body radiation continuous?

    My name is Bradley and I am a first year university student attending Intro to Quantum mechanics lectures but didn't understand... Why the black body radiation curve (unlike the quantized emission seen from atomic spectra), is continuous over all frequencies. I am wondering what exactly gives...
  2. M

    Idea for black body source

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  3. L

    Looking for a critique: reactive black body radiation device

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  4. L

    Sky temperature profiles and black body radiation

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  5. GM Jackson

    How does a black body emit as much energy as it absorbs?

    Homework Statement A black body absorbs all incident electromagnetic radiation, including visible light which has wavelengths from 380nm to 750nm. IR radiation has wavelengths that are so long they are measured in microns. That suggests that visible light has a higher frequency than IR, and...
  6. J

    Black body re-emission of incident radiation

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  7. AdityaDev

    Surface temperature of a planet revolving a sun

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  8. resurgance2001

    Why does the Sun behave like a black body?

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  9. A

    Black Body Radiation: Will it Behave as Perfect Black Body?

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  10. shmijda

    Will a black blob and a white blob glow with the same intensity at 3000 Kelvin?

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  11. M

    Exploring the Quantum Breakthrough: Plank's Formula and Black-Body Radiation

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  12. M

    Black Body Molecular Absorption

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  13. A

    Paint high T, high emissivity for Black Body simulation

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  14. T

    Power Delivered From Black Body

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  15. A

    Black Body Radiation: Get Help Understanding It

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  16. R

    Can a plasma give off black body emission?

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  17. A

    Black body radiation and particle nature of light.

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  18. C

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  19. E

    What Are Black Bodies & Why Are Stars Considered Them?

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  20. gfd43tg

    Does a Black Body Absorb or Release Energy?

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  21. D

    Black Body Radiation at a Distance from Emitter

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  22. applestrudle

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  23. O

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  24. K

    Calculating Spectral Range of Blackbody Radiation Intensity

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  25. F

    Black body radiation and maximum spectral density

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  26. A

    Black Body Radiation: Why Objects Emit Different Wavelengths

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  27. A

    Spectral radiancy curve of a black body

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  28. Overflowing

    Black Body Radiator vs painted surface

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  29. A

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  30. Physics Monkey

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  31. jaumzaum

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  32. M

    Clarification of Black Body Radiation

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  33. N

    Heat lost from face due to black body radiation

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  34. B

    Does a black body radiate all colors of the rainbow?

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  35. S

    Can we see an ideal black body?

    Would an ideal black body be visible to us? What about Ferry's black body? How close was it to an ideal black body?
  36. Crazymechanic

    Exploring the Sun as a Black Body and its Impact on Electromagnetic Radiation

    So as I understand a perfect black body in physics would be one that would absorbs all the radiation wavelengts coming onto it ad let nothing out? If sun is a black body, we all know it emits both visible wavelenght, UV and other.The vast majority of the spectrum being in the visible light...
  37. R

    Frequency of Black body radiation HELP

    If a black body is heated to a temperature T (in degrees K), the most intense radiation is at a wavelength lambda (in m), where λ·T = 2.9×10−3m*K. If the burner on your electric stove is at a temperature of 683K (really hot and glowing), find the wavelength of the most intense black body...
  38. D

    Black Body Radiation: Exploring Radiated & Perpendicular Power

    Can someone help explain what's going on here? http://hyperphysics.phy-astr.gsu.edu/hbase/quantum/radpow.html#c1 Specifically the part about how radiated power is greater than perpendicular power. I also don't understand why the power is being averaged over the various angles. Doesn't it...
  39. E

    How Does a Black Body Balloon Behave in a Vacuum?

    Homework Statement There is a perfectly spherical balloon with surface painted black. It is placed in a perfect vacuum. It is gently inflated with an ideal mono-atomic gas at Kelvin temperature Ti, slowly enough so that it reaches thermal equilibrium with the gas, and then it is sealed off. It...
  40. R

    Can photon-photon interactions alone produce black body radiation?

    Suppose you have a container with perfectly reflecting walls, containing electromagnetic radiation that is not in equilibrium (i.e. does not have a Planck distribution of energies.) Will photon-photon interactions (QED and/or gravitational) produce a Planckian distribution after a sufficiently...
  41. V

    Black body radiation question?

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  42. G

    Degrees of freedom in the energy density formula for black body radiation

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  43. S

    Black Body Radiation: Low Intensity at High & Low Frequqs

    In black body radiation, there are two regions of low intensity. One is at the high frequencies and one is at the low frequencies. I understand that there is lower probability to emit radiation at high frequencies because it requires higher energy than the average thermal energy provided...
  44. fluidistic

    Gray body vs Black body, a few questions

    I have 2 questions. 1)Can a gray body irradiate more than a black body for a given wavelength if both bodies are at the same temperature? 2)If the answer to the previous question is yes, do you know any material that irradiate enough in the visible spectrum that we can see it with our eyes...
  45. N

    What determines frequency of oscillator in black body?

    Hello, If I understand correctly, the main contribution inside solids that result in the behavior of a black body at high temperatures is that the electron clouds vibrate around their nuclei. Please correct me if I'm wrong. If I'm correct: to get a black body spectrum every frequency...
  46. T

    Black Body Radiation: Classical Equipartition vs Boltzmann Distribution

    If you consider the standard cavity experiment for black body radiation, you know that the number of standing wave modes at higher frequencies is higher than the number of modes at lower frequencies. Therefore, according to classical equipartition theorem, there should be more energy in the...
  47. fluidistic

    Spectrum of the Sun vs black body

    In wikipedia I've read that the Sun's surface temperature is about 5700K. The emission spectrum graph can be seen there: http://en.wikipedia.org/wiki/File:EffectiveTemperature_300dpi_e.png. I don't understand why the irradiance (or intensity I guess) of the Sun is greater than the one of a...
  48. S

    How to find the temperature of a black body?

    Homework Statement It emits protons with a frequency of 4 GHz, and has a photon energy of 2.65E-24 J. I tried to use the formula lambda=c/f=vT, but i am somehow getting a negative answer which doesn't make sense when trying to find temperature in (K). Any help is greatly appreciated.
  49. D

    Photons from black body spectra

    Hi, I don't quite understand which are the fundamental processes for production of photons that are emitted by a "black body". Usually this is explained by considering a cavity in thermodynamic equilibrium but I am not interested in this. I am looking for a more practical description of this...
  50. K

    Black Body Radiation & how it works?

    This is just for grasping the concept of the Black Body curve and the UV catastrophe. I don't understand how ideal Black Bodies work? or how they absorb and re-emit the energy which they absorbed? Also, why does radiation bounce around the walls of a cavity of a Black Body? shouldn't the...
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