Sunday, 11 January 2009

Ohm Eddy

A magnet produces a vector field, the magnetic field at all points in the space around it. We are taught that the magnetic field is created by the moving charges in a current-carrying wire. Except I don't believe the charges are in the conductor - hopping and bopping from atom to atom in the metal. In a DC supply, such as a battery, the flow of charge around a circuit is from the positive terminal to the negative terminal (and also vice versa). If there are no charges in the conductor, it means that the 'flow of charge' should actually be acknowledged as the flow of the magnetic field.

If magnetic lines of force (induced by an AC supply) intercept a conducting metal sheet, eddy currents are produced. The eddy currents reduce the intensity of the perpendicular magnetic field at the surface of the conductor. The magnetic field has been converted into electricity by the conductor. The conductor has produced electricity by offering resistance to the magnetic field. Therefore, if no resistance was offered by the conductor to the magnetic field - there would be no electricity - and the magnetic lines of force would pass directly through. (So I wonder if a superconductor is actually representing zero resistance to an electric current. Maybe its offering an incredibly efficient resistance to a magnetic field - so that all the lines of magnetic force are converted into electricity????)

Eddy currents are produced in any core material that is an electric conductor. Eddy currents are the root cause of the skin effect in conductors carrying AC current. I'll go the whole hog and say the eddy currents represent the flow of the magnetic field. In one of Foucault's experiments, a geared-up copper wheel was rotated in the gap of an electromagnet. With no current through the magnet coils the wheel rotated easily. As soon as the magnet was energized (by a DC supply), resistance to rotation was felt and the copper disk started to heat up. In one experiment, the temperature of the disk rose from 10ºC to 61ºC.

So I'm trying to get this straight. The resistance of the conductor converts magnetic force into electricity. The electricity then converts the kinetic energy of the turning wheel into heat. We have magnetic force being converted into heat. Heat is often dismissed by science as proof of inefficiency in the system, because heat cannot be converted back into kinetic energy with 100% efficiency. Some energy from the heat will aways be lost. Wouldn't it be great to find a way of converting heat into kinetic energy with 100% efficiency?

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