Émissivité et absorptivité
A good absorber is always a good emitter, which is why matt black surfaces both heat up fastest in sunlight and cool fastest in the dark. This simulation compares surfaces of different emissivity radiating and absorbing side by side.
Comment utiliser cette simulation
- Choose surfaces from matt black to polished silver
- Set the surface temperature and the surroundings
- Run absorption and emission scenarios
Ce qu’il faut observer
- The best absorber is also the best emitter, every time
- Shiny surfaces both absorb and radiate poorly
- Radiated power depends on the fourth power of temperature, so small temperature rises matter a lot
La physique derrière
Emissivity e measures how well a surface radiates compared with a perfect blackbody, and Kirchhoff's law states that at a given wavelength and temperature the absorptivity equals the emissivity. Radiated power follows the Stefan–Boltzmann law P = eσAT⁴. A perfect blackbody has e = 1; a polished silver surface may be below 0.05.