. Hawkins electrical guide. Questions, answers & illustrations; a progressive course of study for engineers, electricians, students and those desiring to acquire a working knowledge of electricity and its applications; a practical treatise. •:.rr;vE coil ALTERNA-CR PlC 1,300.—Diagram of circuit for example IV. 0MM5 To properly estimate impedance then, in such circuits, thefollowing equation is used: impedance = V resistance -+- (inductance reactance — capacity reactance)* or using symbols, Z = > k: - X,- (3) EXAMPLE IV.—A current has a frequency of 100. It passes througha circuit of 4
. Hawkins electrical guide. Questions, answers & illustrations; a progressive course of study for engineers, electricians, students and those desiring to acquire a working knowledge of electricity and its applications; a practical treatise. •:.rr;vE coil ALTERNA-CR PlC 1,300.—Diagram of circuit for example IV. 0MM5 To properly estimate impedance then, in such circuits, thefollowing equation is used: impedance = V resistance -+- (inductance reactance — capacity reactance)* or using symbols, Z = > k: - X,- (3) EXAMPLE IV.—A current has a frequency of 100. It passes througha circuit of 4 ohms resistance, of 150 milli-benrys inductance, and of 22microfarads capacity. What is the impedance? c. The okmic resistance R, is 4 ohms. b. The inductance reactance, or Xi = 2 r/L = 2 X X 100 X .15 - ohms. ALTERNATING CURRENTS 1,061 SPOOL—>■ Z LAMINATEDIRON CORE. COIL FlG. 1,301.—Simple choking coil. There is an important difference in the obstruction offeredto an alternating current by ordinary resistance and by reactance. Resistance obstructsthe current by dissipating its energy, which is converted into heat. Reactance obstructsthe current by setting up a reverse pressure, and so reduces the current in the circuit,■without wasting much energy, except by hysteresis in any iron magnetized. This may beregarded as one of the advantages of alternating over direct current, for. by introducingreactance into a circuit, the current may be cut down with comparatively little loss ofenergy. This is generally done by increasing the inductance in a circuit, by means ofa device called variously a reactance coil, impedance coil, choking coil, or choker. In thefigure is a coil of thick wire provided with a laminated iron core, which may be eitherfixed or movable. In the fi-st case, the inductance, and therefore alsothe reactance of thecoil, is invariable
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