# Alternating Current Flashcards Flashcards

Terms Definitions
 Alternating Current (AC) An electrical current that constantly changes in amplitude and changes in polarity at regular intervals. Apparent Power That power apparently available for use in an AC circuit containing a reactive element. Average Value of AC The average of all the instantaneous values of one-half cycle of AC. Capacitance The property of an electrical circuit that opposes changes in voltage. Capacitive Reactance (Xc) The opposition offered to the flow of AC by capacitance, expressed in ohms. Capacitor An electrical device capable of storing electrical energy in an electrostatic field. Counter Electromotive Force (CEMF) An electromotive force (voltage) induced in a coil that opposes applied voltage; voltage induced in the coils of a load. Cycle One complete positive and one complete negative alternation of a current or voltage. Dielectric An insulator; the insulating material between the plates of a capacitor. Dielectric Constant The ratio of a capacitance of a capacitor with a dielectric between the electrodes to the capacitance of a capacitor with air between the electrodes. Efficiency The ratio of output power to the input power; generally expressed as a percentage. Effective Value The reading of an alternating current or voltage that will have the same effect on resistance as compared to that of the same value of direct voltage or current on the same amount of resistance. Electromotive Force (EMF) (Voltage) The force that causes electricity to flow between two points with different electrical charges; or when there is a difference in potential between the two points, the unit of measurement is volts. Farad The basic unit of capacitance. A capacitor has a capacitance of 1 farad when a voltage change of 1 volt per second across it produces a current of 1 ampere. Frequency (f) The number of complete cycles per second existing in any form of wave motion, such as the number of cycles per second of an alternating current. Henry (H) The electromagnetic unit of inductance or mutual inductance. The inductance of a circuit is 1 _____ when a current variation of 1 ampere per second induces 1 volt. Impedance (Z) The total opposition offered to the flow of an alternating current. It may consist of any combination of resistance, inductive reactance.
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