GGR203H1 Lecture Notes - Lecture 2: Electric Dipole Moment, Black Body, Energy Flux
Document Summary
2. 3 radiation laws derived from planck function (properties of blackbodies) Emission at all wavelengths increases as t increases. Wavelength at which maximum emission occurs decreases as t increases. At higher temperatures, frequency oscillations, corresponding to shorter wavelength radiation, can be excited. Almost all radiation emitted by sun is at wavelength less than 4. 0 microns; almost all emission from earth is at wavelength greater than 4. 0 microns. Peak sun emission occurs at wavelengths of 0. 5 microns. There is essentially no overlap between emissions of the sun and the earth. Planck function gives maximum amount of emission permitted at a given temperature. As t increases, emission is increasing at all wavelengths. This shifts emissions to shorter wavelengths while total emissions increase. Emissivity is ratio of actual emission to blackbody emission. =1 for a blackbody, otherwise less than 1. Emissivity at a particular wavelength is called the spectral emissivity. Absorption (a): fraction of incident radiation that is absorbed.
