EXAMPLE.—A circuit as shown in fig. 1,330 contains a resistance of 30 ohms, and a capacity of 125 microfarads. If an alternating current of 8 amperes with frequency 60 be flowing in the circuit, what is the ohmic drop, the reactance drop, and the impressed pressure?
The ohmic drop or active pressure is, substituting in formula (1) on page [1,087],
Ea = 30 × 8 = 240 volts
which is the reading of voltmeter A in fig. 1,330.
Fig. 1,331.—Diagram for obtaining the impressed pressure of the circuit shown in fig. 1,330.
The reactance drop or
| I | 8 | |||||
| Ec | = | = | = | 170 volts | ||
| 2πfC | 2 × 3.1416 × 60 × .000125 |
in substituting, note that the capacity C of 125 microfarads is reduced to .000125 farad.
Using a scale of say 1 inch = 80 volts, lay off in fig. 1,331, AB equal to the ohmic drop of 240 volts; on this scale AB = 3 inches. Lay off at right angles, BC = reactance drop = 170 volts = 2.125 inches. Join AC, which gives the impressed voltage, (that is the reading of voltmeter I in fig. 1,330,) which measures 294 volts.