Term
| Definition – alternative current |
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Definition
| a form of current electricity where the polarity of the source periodically changes |
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Term
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Definition
Square wave AC
SAw-tooth AC
sine-wave alternating currnet |
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Definition
(Polarity periodically changes, but “value” does not)
(negative voltage – indicates opposite polarity) |
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Term
| Saw-tooth wave alternating current |
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Definition
| Polarity periodically changes, “value” changes with straight line variation |
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Term
| Sine-wave alternating current (household appliances) |
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Definition
| Polarity periodically changes, “value” changes based on sine function |
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Term
| Generation of (Sine-Wave) AC |
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Definition
a. Created through the principle of (electro) magnetic induction
b. Definition – the creation of an electrical potential (voltage) in a conductor by passing that conductor through lines of magnetic flux
c. Magnetic induction vs. electromagnetic induction
i. Difference is how the lines of flux are produced (if produced by natural magnet – magnetic induction; if produced by electromagnet – electromagnetic induction) |
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Term
| Polarity of Potential (change of positive and negative ends) |
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Definition
a. Based on two things:
i. The orientation of the lines of flux
ii. The direction the conductor is cutting the lines of flux
b. Determined by the “left hand rule” (for generators) figure 4-2
i. Point first finger (“pointer”) in the direction of the lines of flux (flows north to south)
ii. Point thumb in direction of conductor movement
iii. 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) |
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Term
| 5. Increasing Potential (two basic ways) |
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Definition
a. Increase the strength of the flux field being cut
i. Increase the current flow through the electromagnet
ii. Increase the density of the lines of flux
b. Increase the rate at which the lines of flux are cut
i. Increase the speed of the conductor
ii. Increase the number of conductors cutting the flux (wrap conductor into coil) |
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Term
| 6. Advantages/Disadvantages of AC over DC |
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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 distances
d. Not as efficient as DC (does not consistently produce full voltage) |
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Term
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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) |
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Term
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Definition
| one half of a cycle, either in the positive or negative direction |
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Term
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Definition
| time required for one cycle to occur, measure in seconds |
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Term
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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)/120
f = frequency, in hertz
# of poles = magnetic poles (norths and souths)
RPM = conductor rotational speed, per minutes
Note: “period” and “frequency” are numerical inverses of each other |
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Term
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Definition
| the positional relationship between current and voltage, with respect to when each is increasing and decreasing |
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Term
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Definition
| “an immediate increase in one (current or voltage) coincides with an immediate increase in the other” (fig 3-91) |
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Definition
| “any condition other than in-phase” |
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Term
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Definition
| amount of current and voltage are out of phase, in degrees of conductor rotation |
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Term
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Definition
tell which changes first (given with respect to current)
“current leads voltage” or “current lags voltage” (fig 3-90) |
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Term
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Definition
i. The amount of power that would be dissipated in a DC circuit
ii. Given by the formula P = I*E
iii. Apparent power is not an actual power; it is measured in volt-amps |
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Term
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Definition
i. The amount of actual power dissipated in an AC circuit
ii. The amount of true power is determined by amount of phase shift
iii. True power is an actual power; it is measured in watts |
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Term
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Definition
i. Definition – ratio of true power to apparent power
ii. Power factor is given by cos(θ), where θ is the number of degrees of phase shift
iii. PF = PT/PA = cos(θ)
PT = (PA)(PF)
= (I*E)*cos(θ) |
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Term
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Definition
| the maximum instantaneous measure of either current, or voltage, in either the positive or negative direction (fig 3-89) |
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Definition
| the maximum difference between the positive peak and negative peak value |
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Term
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Definition
| the average value of all instantaneous values of one alternation (given by .637 multiplied by the peak value) |
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Term
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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 RMS
a. Significance:
i. It is how we compare AC to DC
ii. It is what we take as our “source voltage”
iii. It is what we read on the multimeter |
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