A few notes
- All bodies with temperature above 0 K emit radiation.
- 0 K = ‒273,15 °C
- A blackbody is a theoretical object that completely absorbs all wavelengths of electromagnetic radiation incident on it.
- When a blackbody is heated to a temperature above 0 K, it emits radiation.
- Blackbody radiation at temperatures comparable to the temperature of the earth’s surface (~300 K) is the thermal infrared (TIR)
- “Good absorbers are good emitters”, meaning that a blackbody emits 100% of the radiation it absorbs (so the absorbed radiation has no effect on the blackbody’s temperature)
It is necessary that the reader understands the following principles.
|Planck’s Law of blackbody radiation||Describes the electromagnetic radiation of a blackbody of a defined temperature|
|Stefan-Boltzmann Law||Calculates the total electromagnetic radiation as function of a blackbody’s temperature|
|Wien’s Displacement Law||Calculates the wavelength at which maximum spectral radiant exitance(emitted radiation) occurs|
|Kirchhoff’s Law||➔Emittance at a given wavelength = absorbance at the same wavelength➔Blackbodies are theoretical; the behaviour of real objects can be described based on how close to being a blackbody they are.➔Emissivity (ε):◆ε = 1 ⇒ blackbody◆ε < 1 ⇒ real-life material|
Planck’s Law of blackbody radiation
- Created by Max Planck (1858–1947)
- Blackbody radiation can be calculated by the object’s (absolute) temperature according to the formula:
- λ: wavelength
- Mλ: radiation at wavelength λ
- Τ: temperature (absolute temperature in K).
Therefore, at any given wavelength we can have a spectral radiant exitance curve (“radiation”) according to the absolute temperature:
(to be continued)