polarityAlso see bipolar signaling and unipolar signaling . Polarity is a term used in electricity, magnetism, and electronic signaling. Suppose there is a constant voltage , also called an electric potential or electromotive force (EMF), between two objects or points. In such a situation, one of the objects or points (poles) has more electrons than the other. The pole with relatively more electrons is said to have negative polarity; the other is assigned positive polarity. If the two poles are connected by a conductive path such as a wire, electron s flow from the negative pole toward the positive pole. This flow of charge carriers constitutes an electric current . In physics, the theoretical direction of current flow is considered to be from positive to negative by convention, opposite to the flow of electrons. The movement of electric charge carriers inevitably produces a magnetic field. Conversely, any magnetic field is the result of the motion of charge carriers. In a permanent magnet, a magnetic field is produced by the composite motions of electrons in geometrically aligned atom s. A magnetic field is characterized by poles called north and south. Magnetic polarity refers to the orientation of these poles in space. In digital communications, data is composed of short-duration pulses called bit s (binary digits). There are two possible states for each bit: logic 0 (also called low) and logic 1 (also called high). In a closed circuit, these logic elements are represented by direct current voltages. A high-speed data signal varies rapidly between the low and high states. Common values are approximately +0.5 volts for low and +5 volts for high. In some cases different values are used, for example, -3 volts for low and +3 volts for high, or -5 volts for low and -0.5 volts for high. If both voltages have the same polarity, the signal is called unipolar; if the voltages have opposite polarity, the signal is called bipolar.
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Sep 21, 2005 |
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