Ques. What effect has lag or lead on the value of the effective current?
Ans. As the angle of lag or lead increases, the value of the effective as compared with the virtual current diminishes.
Reactance.—The term "reactance" means simply reaction. It is used to express certain effects of the alternating current other than that due to the ohmic resistance of the circuit. Thus, inductance reactance means the reaction due to the spurious resistance of inductance expressed in ohms; similarly, capacity reactance, means the reaction due to capacity, expressed in ohms. It should be noted that the term reactance, alone, that is, unqualified, is generally understood to mean inductance reactance, though ill advisedly so.
The resistance offered by a wire to the flow of a direct current is expressed in ohms; this resistance remains constant whether the wire be straight or coiled. If an alternating current flow through the wire, there is in addition to the ordinary or "ohmic" resistance of the wire, a "spurious" resistance arising from the development of a reverse pressure due to induction, which is more or less in value according as the wire be coiled or straight. This spurious resistance as distinguished from the ohmic resistance is called the reactance, and is expressed in ohms.
Reactance, may then be defined with respect to its usual significance, that is, inductance reactance, as the component of the impedance which when multiplied into the current, gives the wattless component of the pressure.
Reactance is simply inductance measured in ohms.
Fig. 1,294.—Diagram of the circuit for example I. Here the resistance is taken at zero, but this would not be possible in practice, as all circuits contain more or less resistance though it may be, in some cases, negligibly small.
EXAMPLE I.—An alternating current having a frequency of 60 is passed through a coil whose inductance is .5 henry. What is the reactance?
Here f = 60 and L = .5; substituting these in formula for inductive reactance,