# Shared Flashcard Set

## Details

Fundamental Electricity Quiz
Quiz
25
Aviation
Professional
02/20/2012

Term
 Definition – alternative current
Definition
 a form of current electricity where the polarity of the source periodically changes
Term
 Three common AC forms
Definition
 Square wave ACSAw-tooth ACsine-wave alternating currnet
Term
 Square wave AC
Definition
 (Polarity periodically changes, but “value” does not)(negative voltage – indicates opposite polarity)
Term
 Saw-tooth wave alternating current
Definition
 Polarity periodically changes, “value” changes with straight line variation
Term
 Sine-wave alternating current (household appliances)
Definition
 Polarity periodically changes, “value” changes based on sine function
Term
 Generation of (Sine-Wave) AC
Definition
 a. Created through the principle of (electro) magnetic inductionb. Definition – the creation of an electrical potential (voltage) in a conductor by passing that conductor through lines of magnetic fluxc. Magnetic induction vs. electromagnetic inductioni. Difference is how the lines of flux are produced (if produced by natural magnet – magnetic induction; if produced by electromagnet – electromagnetic induction)
Term
 Polarity of Potential (change of positive and negative ends)
Definition
 a. Based on two things:i. The orientation of the lines of flux ii. The direction the conductor is cutting the lines of fluxb. Determined by the “left hand rule” (for generators) figure 4-2i. Point first finger (“pointer”) in the direction of the lines of flux (flows north to south)ii. Point thumb in direction of conductor movementiii. Middle finger will point in the direction of current flow (EMF)“the middle finger will point to the negative potential”(will point to the negative of the source – where the electrons)(x in circle means far end is negative; dot in circle means near end is negative)c. (As source passes through 180° point: “increasing potential (voltage) in the negative polarity”)(numbers indicate degrees of conductor rotation)
Term
 5. Increasing Potential (two basic ways)
Definition
 a. Increase the strength of the flux field being cuti. Increase the current flow through the electromagnetii. Increase the density of the lines of fluxb. Increase the rate at which the lines of flux are cuti. Increase the speed of the conductorii. Increase the number of conductors cutting the flux (wrap conductor into coil)
Term
Definition
 a. Much easier to generate large quantities (either voltages or currents)b. Much easier to change “values” without substantial power loss*c. Much easier to transfer over long distancesd. Not as efficient as DC (does not consistently produce full voltage)
Term
 Cycle Defined
Definition
 one complete sequence of events (of either current or voltage) from zero, to the positive peak, to zero, to the negative peak, and back to zero (fig 3-88)
Term
 Alternation - defined
Definition
 one half of a cycle, either in the positive or negative direction
Term
 Period - defined
Definition
 time required for one cycle to occur, measure in seconds
Term
 Frequency
Definition
 the number of cycles per second, measured in hertz(frequency and period inversely related)Formula: f = (# of poles/2) * (RPM/60) = (# of poles)(RPM)/120f = frequency, in hertz# of poles = magnetic poles (norths and souths)RPM = conductor rotational speed, per minutesNote: “period” and “frequency” are numerical inverses of each other
Term
 Phase - defined
Definition
 the positional relationship between current and voltage, with respect to when each is increasing and decreasing
Term
 in-phase
Definition
 “an immediate increase in one (current or voltage) coincides with an immediate increase in the other” (fig 3-91)
Term
 out-of-phase
Definition
 “any condition other than in-phase”
Term
 phase shift
Definition
 amount of current and voltage are out of phase, in degrees of conductor rotation
Term
Definition
 tell which changes first (given with respect to current) “current leads voltage” or “current lags voltage” (fig 3-90)
Term
 apparent power
Definition
 i. The amount of power that would be dissipated in a DC circuitii. Given by the formula P = I*Eiii. Apparent power is not an actual power; it is measured in volt-amps
Term
 true power
Definition
 i. The amount of actual power dissipated in an AC circuitii. The amount of true power is determined by amount of phase shiftiii. True power is an actual power; it is measured in watts
Term
 power factor
Definition
 i. Definition – ratio of true power to apparent powerii. Power factor is given by cos(θ), where θ is the number of degrees of phase shiftiii. PF = PT/PA = cos(θ)PT = (PA)(PF) = (I*E)*cos(θ)
Term
 peak value
Definition
 the maximum instantaneous measure of either current, or voltage, in either the positive or negative direction (fig 3-89)
Term
 peak to peak value
Definition
 the maximum difference between the positive peak and negative peak value
Term
 average value
Definition
 the average value of all instantaneous values of one alternation (given by .637 multiplied by the peak value)
Term
 effective (RMS) value
Definition
 – the amount of DC that is capable of dissipating the same amount of heat as a given sine-wave AC (given be .707 peak value)***Also known as Root Mean Square, or RMSa. Significance:i. It is how we compare AC to DCii. It is what we take as our “source voltage”iii. It is what we read on the multimeter
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