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Page 1081 | Volume 4 | Chapter 47 | Alternating Current Diagrams

In some problems it is required to find the impedance of a circuit in which the ohmic and spurious resistances are given. This is done in a manner similar to finding the impressed pressure.

Ohmic resistance and spurious resistance or inductance reactance both tend to reduce an alternating current. Their

Fig. 1,322. - Graphical method of obtaining the impedance in circuits containing resistance and inductance, having given the resistance and reactance, that is, the ohmic resistance and spurious resistance.
Fig. 1,322.—Graphical method of obtaining the impedance in circuits containing resistance and inductance, having given the resistance and reactance, that is, the ohmic resistance and spurious resistance. With any convenient scale layoff AB = resistance, and erect the perpendicular BC = reactance (using the same scale); join AC, whose length (measured with the same scale) will give the impedance.

combined action or impedance is equal to the square root of the sum of their squares, that is,

impedance = √resistance2 + reactance2

This relation is represented graphically by the side of a right angle triangle as in fig. 1,322, in which the hypothenuse corresponds to the impedance, and the sides to the resistance and reactance.

EXAMPLE.—In a certain circuit the resistance is 4 ohms, and the reactance 3 ohms. What is the impedance?


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