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.
You heat an ideal material (solid, liquid, gas) and it emits electromagnetic radiation, with a spectral energy distribution (SED) following that of a "black body", per Planck.
You heat a homogeneous real material (a lump of iron, a body of water, some hydrogen; things like dust with a wide...
can i ask ... how could Planck's idea of quantised energy explain the ultraviolet catastrophe?
WHAT is being quantised? the oscillator atoms of the blackbody cavity? or?
thanks
Hi i was just wondering you when black bodies emit all spectrum of electromagnetic radiation. Now are atmosphere absorbs a particular part, therefore the peak wavelength and temperature appear to be different according to the rules of wiens law. Now does Earth atmosphere absorb Shorter...
If the sun at temperature 6000K emits onto an asteroid 350million km away, what is the temperature of the asteroid assuming it is a black body?
Any suggestions how to go about this please? :confused: :confused:
My problem is that I have the numbers...but I don't have a formula.
"The sun's temp. is about 6000 K, it's radius 700000 km. How much power is it radiating? If there is no dissipation between here and the sun, how much of this hits the earth?"
Is this the P = c/4*U thing?
Hello,
New to this message board (and very happy to have found it).
I am reading a book on cosmology by Steven Weinberg... I am having a terrible time understanding what exactly black body radiation is. Could someone please describe it in the most accesible terms? Also, if you would please...
Hi,
In one of my textbooks, I'm given these two equivalent equations for energy flux radiated from a black body, one dependent on frequency, the other on wavelength:
I(\lambda)d\lambda = \frac {2c^2h}{\lambda^5} \frac {1}{e^{(hc/KT\lambda)}-1}d\lambda
and
I(\nu)d\nu = \frac...