A diagram is unnecessary in obtaining the impressed pressure since it is simply the difference between inductance pressure and capacity pressure (the circuit being assumed to have no resistance), that is
impressed pressure = Ei - Ec = 377 - 255 = 122 volts.
EXAMPLE.—A circuit in which a current of 20 amperes is flowing at a frequency of 100, has an inductance reactance of 18.25 ohms, and a capacity of 125 microfarads. What is the impedance?
The reactance due to capacity is
| 1 | 1 | |||||
| Xc | = | = | = | 12.76 ohms. | ||
| 2πfC | 2 × 3.1416 × 100 × .000125 |
The impedance of the circuit then is the difference between the two reactances, that is impedance = inductance reactance - capacity reactance, or
Z = Xi - Xc = 18.25 - 12.76 = 5.49 ohms.
Fig. 1,335.—Impedance diagram for circuit (of above example) containing inductance and capacity. With any convenient scale, erect a perpendicular AB = 18.25 ohms, and CD = 12.76 ohms. Continue CD by dotted line to D' so that CD' = AB, then DD' = AB - CD = inductance reactance - capacity reactance, which is equal to the impedance. Expressed by letters Z = Xi - Xc = DD', which by measurement = 5.49 ohms.
Circuits Containing Resistance, Inductance, and Capacity.—When the three quantities resistance, inductance, and capacity, are present in a circuit, the combined effect is easily understood by remembering that inductance and capacity always act oppositely, that is, they tend to neutralize each other. Hence, in problems involving the three quantities, the resultant of inductance and capacity is first obtained, which, together with the resistance, is used in determining the final effect.