Circuits Containing Inductance and Capacity.—The effect of capacity in a circuit is exactly the opposite of inductance, that is, one tends to neutralize the other. The method of representing each graphically has been shown in the preceding figures. Since they act oppositely, that is 180° apart, the reactance due to each may be calculated and the values thus found, represented by oppositely directed vertical lines: the inductance resistance upward from a reference line, and the capacity resistance downward from the same reference line. The difference then is the resultant impedance. This method is shown in fig. 1,332, but it is more conveniently done as in fig. 1,333.
Fig. 1,334.—Diagram of circuit containing 30 milli-henrys inductance and 125 microfarads capacity, with current of 20 amperes, 100 frequency.
EXAMPLE.—In a circuit, as in fig. 1,334, containing an inductance of 30 milli-henrys and a capacity of 125 microfarads, how many volts must be impressed on the circuit to produce a current of 20 amperes having a frequency of 100.
The inductance reactance is
Xi = 2πfL = 2 × 3.1416 × 100 × .03 = 18.85 ohms.
Substituting this and the current value of 20 amperes in the formula for inductance pressure
Ei = RiI = 18.85 × 20 = 377 volts.
Reducing 125 microfarads to .000125 farad, and substituting in the formula for capacity pressure
| I | 20 | |||||
| Ec | = | = | = | 255 volts. | ||
| 2πfC | 2 × 3.1416 × 100 × .000125 |