Electromagnetic field: Encyclopedia II - Electromagnetic field - Source and Sinks

Electromagnetic field - Source and Sinks

Electric charges act either as sources or sinks of the electric fluid. An electron is constantly absorbing electric fluid around it at some rate, call it ε. Protons are the reverse: they constantly pour electric "fluid" towards the surrounding space at rate ε, so fluid moves away from the proton with speed

(where r is distance of the fluid away from the proton) so that the total flux of fluid going through any (imaginary) sphere which contains that proton is the area of the sphere times the speed of the fluid flowing through it: .

Electromagnetic field - The two fluids

Magnetic fluid, on the other hand, has no sources or sinks: there are no magnetic charges that could pour out or suck up magnetic fluid. If magnetic fluid is standing still, it can be stirred up, making it move in closed circles and closed loops (see vortical motion).

For a magnetic fluid to keep moving in the same loop, though, some force has to keep stirring it up: otherwise the energy of its circular motion will dissipate and the magnetic fluid will stop moving and will return to rest.

Electromagnetic field - The vortex

If electric fluid starts to accelerate in a certain direction, it will cause a vortex of magnetic fluid to move in circles around the direction in which the electric fluid is accelerating (according to the right hand rule). As soon as the electric fluid stops accelerating, the vortex of magnetic fluid vanishes.

Notice that electric fluid will not accelerate spontaneously; something has to force it to accelerate. This same thing then indirectly causes the magnetic vortex to be stirred up: a magnetic vortex will not arise spontaneously.

Finally, if magnetic fluid accelerates in a certain direction, it causes electric fluid to move in a vortex which circles around the direction of acceleration in the direction opposite to the right hand rule.

Electromagnetic field - Summary

To summarise, an acceleration of the electric fluid causes a positive vortex of magnetic "fluid" to move around it, but an acceleration of the magnetic fluid causes a negative vortex of electric fluid to flow around it.

Electromagnetic field - Negative Feedback Loop

The opposite signs of acceleration create a negative feedback loop (see Lenz's law.) An acceleration of electric fluid causes a positive magnetic vortex. This means that the magnetic fluid has been accelerated to produce this circular flow. But this causes a negative vortex of electric fluid around the magnetic vortex. This reactive vortical acceleration of electric fluid is in the direction opposite of the original acceleration of electric fluid: hence a negative feedback loop:

Electromagnetic field - Positive Feedback Loop

If there were a positive feedback loop, the result might be similar to the high pitched resonant effect produced by a microphone too close to its speaker. The positive feedback would cause the original acceleration of electric fluid to amplify itself continually, while at the same time the vortices around it would amplify as well: an explosive maelstrom of movement of the laws of electromagnetism and conservation of energy being what they are, an initial disturbance (acceleration) of the electric fluid will cause a feedback loop that, being negative, will tend to extinguish itself at its source but which will propagate outwards in what is called an electromagnetic wave.

Adapted from the Wikipedia article "Source and Sinks", under the G.N U Free Docmentation License. Please also see http://en.wikipedia.org/wiki