fra0300 Basic Electroincs

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The discovery by Hans C. Oersted in 1820, that a compass needle is deflected when placed near an electric current was of fundamental importance in that it immediately suggested a connection between electricity and magnetism. The magnet (needle) returned to its original position as soon as the current was zero, or the needle was deflected in the opposite direction if the current was reversed. Since, by definition, a magnetic field is a region where forces act on magnets, you can imply that a magnetic field surrounds the current-carrying conductor. The magnetic field may be represented by line of force as previously mentioned. As with permanent magnets, you can indicate the nature of the field about any shaped conductor with iron filings.

By exploring the field around a very long conductor with a tiny compass needle, you will find that the lines of force are circles with their centers in the wire (see figure 1-17A). A convenient method of remembering the direction of the field about a wire is to recall the left-hand rule. If you mentally grasp the wire with the left hand, holding the extended thumb in the direction of the electron flow, your fingers circle the wire in the direction of the magnetic field.


David L. Heiserman, Editor

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Revised: June 06, 2015