M 4 R

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Fig. 24-1 Ohm's Law Relationships.

Fig. 24-1 Ohm's Law Relationships.

Reactance is the measure (in ohms) of opposition to the flow of alternating current. Capacitive reactance is the opposition offered by capacitors and inductive reactance is the opposition offered by an inductive load.

Magnetism concerns magnetic fields and their effects on materials. A magnet establishes a field around itself that can be graphically represented by directed lines, i.e., magnetic lines of force (or flux). When an electric current passes through a conductor, a magnetic field surrounds the conductor. This is electromagnetism.

When a conductor is wound into a coil, the field around each turn in the coil interacts with the other turns. The net result is a large number of long parallel lines of flux running down the axis of the coil and creating a large field around the coil. Such a coil is known as an electromagnet. As shown graphically in Figure 24-2, lines of force, or magnetic flux, are considered to leave the magnet's north (N) pole, travel externally, and re-enter the magnet at its south (S) pole.

Fig. 24-2 Magnetic Flux.

According to Faraday's Laws, when a conductor (or coil) is moved through a magnetic field, a current is produced in the conductor. This current is said to be induced. Thus, the operative principle for electric motor, generator, and transformer action is called electromagnetic induction.

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