Share
Explore BrainMass

Blackbody Radiation

Black-body radiation is a type of electromagnetic radiation within or surrounding a body in thermodynamic equilibrium with its environment or emitted by a black body held at constant, uniform temperature. The radiation has a specific spectrum and intensity that depends only on the temperature of the body.

A perfectly insulated enclosure that is in thermal equilibrium internally contains black-body radiation and will emit it through a hole made in its wall, provided that hole is small enough to have negligible effect upon that equilibrium.

A black-body at room temperature appears black, as most of the energy it radiates is infra-red and cannot be perceived by the human eye. At higher temperature, it glows with increasing intensity and colors that will range from dull red to blindingly blue-white as the temperature increases.
Planck’s law of black-body radiation states

I(v,T)= (2hv^3)/c^2 1/(e^(hv/kT)-1)

Where I(v,T) is the energy per unit time radiated per unit area of emitting surface in the normal direction per unit soli angle per unit frequency by a black body at temperature T
H is the Planck constant
C is the speed of light in a vacuum
K is the Boltzmann constant
V is the frequency of the electromagnetic radiation
T is the absolute temperature of the body

Wien’s displacement law shows how the spectrum of black-body radiation at any temperature is related to the spectrum at any other temperature. A consequence of Wien’s displacement law is that the wavelength at which the intensity per unit wavelength of the radiation produced by a black body is at a maximum λmax which is a function of only temperature as seen below:

λ_max=b/T

Where b is the Wien’s displacement constant.

The Stefan-Boltzmann Law states that the power emitted per unit area of the surface of a black body is directly proportional to the fourth power of its absolute temperature as seen below:

j^*= σT^4

Where j* is the total power radiated per unit area, T is the absolute temperature and σ is the Stefan-Boltzmann constant

Planck's formula for spectral distribution

Planck's formula for spectral distribution of the flux emitted by a blackbody is: S_v = [(2*pi*h)/(c^2)][(v^3)/((e^hv/kT)-1)] a) from this formula deduce that the totl flux is proportional to the fourth power of the temperture, that is: integral from 0 to infinity S_v dv (proportionality symbo

Classical theory is energy radiated by a blackbody approached

Please see attached for all questions. 1. According to the classical theory of physics, the energy radiated by a blackbody approached infinity as the wavelength of the emitted light approaches zero. a) Why is this considered a problem for classical physics? b) Max Planck solved this problem is 1990. What was the key to th

Planck's Law for Blackbody Radiation vs. The Rayleigh-Jeans Law

Given: f(lambda) = 8pi*kt(lambda^4) Where lambda is measured in meters, T is the temperature in kelvins, k is Boltzmann's constant. The Rayleigh-Jeans Law agrees with experimental measurements for long wavelengths but disagrees drastically for short wavelengths. [The law predicts that f(lambda) -> 0 as f(lambda) --> infinity