Radiation

Radiation
Thermal radiation.:
”That electromagnetic radiation emitted by a body as a result of its temperature”.

Thermal radiation is restricted to a limited range of the electromagnetic spectrum.

Blackbody radiation
A blackbody is a perfect radiator.
Three characteristics:
• It absorbs all incident radiation
• It radiates more energy than any real surface at the same temperature
• The emitted radiation is independent of direction
Also:
Blackbody radiation obey certain simple laws

Stefan-Boltzmann’s law
The total power radiated from a blackbody is calculated from Stefan-Boltzmann´s law:
Eb = σ⋅T4
where Eb = total power radiated per unit area from
a blackbody (W/m2)
σ = 5.669 ⋅ 10-8 W/(m2⋅K4). (Stefan-Boltzmann
constant)
T = absolute temperature (K)

Planck distribution law
The wavelength distribution of emitted blackbody radiation is determined from the Planck distribution law:
[]ETCCTbλλλλ,(,)exp(/())=⋅⋅1521−
where C1 = 2π⋅h⋅co2 = 3.742⋅108 W⋅μm4 / m2
C2 = (h⋅co / k) =1.439 ⋅ 104 μm K
λ = wavelength (μm)
T = absolute temperature (T)
h = Planck constant



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