Electromagnetic waves are generated by moving electrons. An electron generates an electric field which we can visualize as lines radiating from the electron Figure 10a. If the electron moves, say it vibrates back and forth, then this motion will be transferred to the field lines and they will become wavy Figure 10b. In turn, the moving electron generates a magnetic field that will also become wavy from the motion of the electron. These combined electrical and magnetic waves reinforce one another. This kind of wave is called an electromagnetic wave and light is such a wave. Since all matter contains electrons and all these electrons are in motion, as are the atomic nuclei they spin around, all matter generates electromagnetic waves. Since all electromagnetic waves travel at the same speed (c) the frequency of the waves is determined by the frequency of the vibrating electrons that generate them. Hot substances have more energy and their component atoms vibrate more rapidly than those of cold bodies. Thus the peak energy radiated by hot bodies has a higher frequency, shorter wavelength, than that of cooler bodies. The relationship of the peak frequency of a black body to its absolute temperature is expressed by Wein's Law.
lmax = a/T
a = 2989 if l is measured in microns
Electromagnetic (EM) radiation is emitted by all matter and consists of orthogonal electrical and magnetic waves. All EM travels at the same speed through a vacuum (186,000 miles per second or 300,000 kilometers per sec.). This radiation is generated by a moving charge or charges. All matter consists of atoms in motion and these in turn consist of positively charged protons surrounded by a cloud of negatively charged electrons. The vibrating motion of the atoms causes the cloud of electrons to oscillate and this oscillation generates electromagnetic radiation. Since all electromagnetic radiation travels at the same velocity the frequency and wavelength of the generated radiation depends on the frequency of the oscillating electron cloud. Thus, on average, cool objects (say those at room temperature) generate long wavelength (low frequency) radiation, while hot objects (such as the sun) generate short wavelength (high frequency) radiation.