Stefan-Boltzmann Law Vocabulary

Flashcards covering the definitions, constants, and formulas related to the Stefan-Boltzmann Law of radiation.

Stefan-Boltzmann Law

A law stating that the total amount of heat energy radiated per second per unit area of a perfectly black body is directly proportional to the fourth power of its absolute temperature.

Stefan's constant ($\sigma$) in SI-units

A proportionality constant with a value of $5.67 \times 10^{-8}\,watt\,m\,K$.

Stefan's constant ($\sigma$) in CGS-system

A proportionality constant with a value of $5.67 \times 10^{-5}\,erg\,s^{-1}\,cm^{2}\,K$.

Power ($P$) radiated by area $A$

The energy per second radiated by a black body of area $A$, expressed by the formula $P = \sigma AT^4$.

Thermal equilibrium

The state eventually reached when bodies absorb heat radiation from surrounding objects to match the temperature of the environments.

$$E_{emit}$$

The heat energy radiated per second per unit area by an object at absolute temperature $T_1$, defined as $E_{emit} = \sigma T_1^4$.

$$E_{abs.}$$

The heat energy absorbed per second per unit area by a body placed inside an enclosure at absolute temperature $T_0$, defined as $E_{abs.} = \sigma T_0^4$.

$E_{net}$ (Net loss of heat energy)

The net loss of heat energy per unit area per second by an object, calculated as $E_{net} = \sigma (T_1^4 - T_0^4)$, where $T_1 > T_0$.

Emissivity ($e$)

A factor used for bodies that are not perfectly black, modifying the Stefan-Boltzmann equation to $E = \sigma e T^4$.

Emissivity ($e$) of a perfectly black body

The value of $e$ for a perfectly black body is $1$.

$E_{net}$ for a body with emissivity $e$

The net loss of heat energy per unit area per second for a non-perfectly black body, calculated as $E_{net} = \sigma e (T_1^4 - T_0^4)$.