Instances of this effect are commonly met with in connection with transformers. Since the primary coil of a transformer has a high reactance, very little current will flow when an alternating pressure is applied. If the same transformer were placed in a direct current circuit and the current turned on it would at once burn out, as very little resistance would be offered and a large current would pass through the winding.
Fig. 1,296.—Diagram of circuit for example III.
EXAMPLE III.—In a circuit containing only capacity, what is the reactance when current is supplied at a frequency of 100, and the capacity is 50 microfarads?
| 1 | ||||||
| 50 microfarads | = | 50 | × | = | .00005 farad | |
| 1,000,000 |
capacity reactance, or
| 1 | 1 | |||||
| Xc | = | = | = | 31.84 ohms | ||
| 2πfC | 2 × 3.1416 × 100 × .00005 |
Impedance.—This term, strictly speaking, means the ratio of any impressed pressure to the current which it produces in a conductor. It may be further defined as the total opposition in an electric circuit to the flow of an alternating current.
All power circuits for alternating current are calculated with reference to impedance. The impedance may be called the combination of:
- Ohmic resistance;
- Inductance reactance;
- Capacity reactance.