## 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)

### Basic principles

It is necessary that the reader understands the following principles.

PRINCIPLE | DESCRIPTION |

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:

where

- 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)*