Emission (electromagnetic radiation)
From ArticleWorld
Electromagnetic emission refers to the radiation energy that is emitted whenever electric charges accelerate; this may involve a change in their speed or the direction of their motion. An example of emission is that of light during wave propagation. This is often termed as radiation.
Electromagnetic radiation is basically understood as a wave that can propagate itself anywhere in space, possessing both electric and magnetic components. These components oscillate at right angles to the direction of propagation and to each other as well. They are in phase with each other as well.
The mechanisms of electromagnetic emissions
The different frequencies when put under observation can give a lot of information about the source of electromagnetic radiation, as also the media of propagation. Electromagnetic radiation can be produced by both mechanisms that involve heat and by those that do not involve heat. Examples of the first case include the continuous spectrum emission that is related to the temperature of an object and the specific frequency emissions that arise from neutral hydrogen.
Examples of non-thermal mechanisms of electromagnetic emissions include emissions due to synchrotron radiation and amplified emissions due to astrophysical masers, which are essentially natural sources of stimulated spectral line emission and are found in the microwave section of the electromagnetic spectrum.
Thermal radiation
Every object that possesses heat energy emits it out as radiation. Any body that is heated above the absolute zero temperature gives out electromagnetic emissions. The energy is emitted at all frequencies and at the same rate that it is absorbed.
The kind of radiation that is emitted by matter at a particular frequency band is directly dependant on the temperature that they possess. In any hot object, molecules are in a state of continuous vibration (in solids) or constantly colliding against each other (in a liquid or a gas). This causes the electrons to be sent off in various directions, causing electromagnetic radiation at all frequencies in the electromagnetic spectrum. Examples of such radiation are infrared radiation, visible light and ultraviolet radiation from the sun.
Shorter the wavelength and higher the frequency, greater is the energy possessed by the radiation.
Non-thermal radiation
Radiation can also be produced by mechanisms unrelated to the temperature of an object. Such radiation arises from the effect of the interaction of charged particles with magnetic fields. Electromagnetic radiation is initiated by the acceleration of the charged particle in a neighboring magnetic field, which forces it to move spirally around the magnetic lines of force. The intensity of non-thermal electromagnetic emission usually decreases with frequency, in contrast with the case of thermally caused electromagnetic emission.
An example of such radiation is seen in the phenomenon of quasars, which emit radiation in the radio, visible and x-ray spectra. Such radiation is referred to as synchrotron radiation, when the particles that give rise to it nearly achieve the speed of light.