EM 1110-2-2907
1 October 2003
(1) Wien's Displacement Law. In Equation 2-2 wavelength is shown to be an in-
verse function of energy. It is also true that wavelength is inversely related to the tem-
perature of the source. This is explained by Wein's displacement law (Equation 2-3):
Lm = A/T
(2-3)
where
Lm = maximum wavelength
A = 2898 m Kelvin
T = temperature Kelvin emitted from the object.
Using this formula (Equation 2-3), we can determine the temperature of an object by
measuring the wavelength of its incoming radiation.
by a human?
Solution: Solve for Lm given T from Table 2-1
Calculation: T = 98.6oC or 310 K (From Table 2-1)
A = 2898 m Kelvin
Lm = 2898 m K/310K
Lm =9.3 m
this is well beyond what the eye is capable of seeing. Humans
can see in the visible part of the electromagnetic spectrum at
wavelengths of 0.40.7m.
(2) The Stefan-Boltzmann Law. The Stefan-Boltzmann Law states that the total en-
ergy radiated by a black body per volume of time is proportional to the fourth power of
temperature. This can be represented by the following equation:
M = σ T4
(2-4)
where
M =
radiant surface energy in watts (w)
Stefan-Boltzmann constant (5.6697 10-8 w/m2K4)
σ =
T =
temperature in Kelvin emitted from the object.
2-12
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