Alternating Current Flashcards by Zachary Chow

As the loop approaches 90 degrees of rotation the flux lines are cut at a ___ rate (more voltage, voltage peak)

faster

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Induced voltage at 45 degree angle is ___

70.7 volts

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RMS = actual ___ value

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Skin effect in AC circuits

frequency goes ___, skin effect goes ___

Large CMA, Resistance goes ___

up, up

down

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Skin effect = ___

tendency of electrons to move towards outside of conductor

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phase = current rise and falls at the ___ rate as voltage, and reverses in polarity the ___ as well. (reverse flow)

same

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resistive loads - contain pure ____

-produce heat
-current and voltage are in ___ with each other

resistance, phase

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___ circuit - electrons travel through entire conductor

___ circuit - electrons forced outside conductor (skin effect)

DC, AC

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ripple - pulsating DC - turns on and off but never changes ___

polarity

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Inductive capacitance - ___

Impedance - ___

Inductive reactance (__)
(inductance H or L) (reactance X)

farads, ohms, XL

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XL (inductive reactance) = ___

2 pie f length

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Each is 63.5 (5 of them)

100 - 63.5 = 36.8

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Inductance in AC circuits

____ = AC load, usually with coil

motors, transformers, lightning ballast, and chokes

Inductance (L)

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Impedance rules: (4 of them)

1) cutting of magnetic flux through coil, induce voltage
2) Induced voltage ___ in polarity to applied voltage (CEMF) (Counter Electromotive Force)
3) # amount of induced voltage proportional to ___ of current change
4) An inductor opposes a change of ___

opposite, rate, current

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Voltage goes up, current change goes up

True or False

True

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An inductor opposes a change of current

True or False

True

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Inductors connected to AC voltage
-induced voltage is ___ degrees out of phase with applied voltage and opposition to applied voltage

currents flow (out)
decrease (collapse)

180

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E (INST) = the voltage at any point on the wave form

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___ = impedance (ohms) (h = z)
___ = Reactance in ohms (y = o)
___ = Resistance in ohms (x = a)

Z ,X, R

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___ = Apparent power (VA) (h=z)
___ = Reactive power (VARS) (y = o)
___ = True power (Watts) (x = a)

VA, VARS, Watts

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____ = AVR (E, I)
____ Effective (E, I)
____ (Pav, P)

Instantaneous (lower case) = sin (theta)
AVR = 0.637
Effective (RMS) = 0.707 (E, I)
Effective (RMS) = 0.5 (P)

Em = Blv
Im = EM/R
Pm = Em x Im

0.637, 0.707,, 0.5

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Capital (m) = max
Capital = Effective
lower case = instantaneous
AVR = average

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AVR (av) = full cycle = 0

Everything basically calculated by peak (Pm = Im x Rm) or

Effective (capital) P = E power of 2 / R

to get resistance (ohms)

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60 cycles per 1 sec = 60 Hz

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oscilloscope = see ripple voltages add

Magnetic Induction ____ = rate of certain occurences. current rise 63.2 percent each time constant (5 times constant)

Exponential curve

high permeability (silicon, steel, and soft iron) low permeability (brass, copper, or aluminium)

Induced voltage spike voltage spike - current flow stops and decrease. - suppressed by ___ (MOV) Diode = permits current flow in only one direction

Metal Oxide Varistor

Inductance in AC circuit Inductance - creates voltage by change to ____ (reverse polarity) or increase or decrease of ___ in different directions. & magnitude (direction of armature rotation) - speed of rotation faster, more induced voltage

magnetic field, current

Lenz's law - an induced voltage or current opposes the motion that causes it -___ always oppose a change in current

Inductors

Vertical = 180 degrees and 360 degrees Flat (parallel) = 270 degrees and 90 degrees shunt - field pole coil

Magnetic Inductance Amount of Voltage Induced in a conductor 1) The number of turns of wire 2) The strength of the magnetic field (flux density) 3) The speed of the cutting action

Solenoid = converts energy (____) to ____ uses relay

(electrical), mechanical

Impedance (ohms) =(inductive and capacitance)

Hz = (# poles x RPM) / 120

T (time, secs) = L (Henry, Inductance) / R (resistance)

XL = ___ Inductive reactance, proportional to inductance) = constant x pie x frequency in hertz (Hz) x inductance in henrys (H) proportional to: - # of turns of wire - strength of magnetic field - the speed of cutting action (relative motion between inductor & magnetic lines of flux)

2 pie f L

Terms (symbol) (unit) Reactance (X) (ohms) Inductance (L) H) capacitance (C) (F) Inductive reactance (XL) (ohms) Capacitive reactance (XC) (Farads) Impedance (Z) (ohms)

E (INST) = voltage at any point on the wave form

Wave forms (3 of them) (Sine Wave, Square Waves, and Triangle waves)

Oscillators = produce Square waves

___ = a triangle wave (voltage rise at a constant rate with respect to time)

linear wave

Sine wave - contains 360 degrees each complete 360 degree is called a cycle frequency = # number of complete cycles in one second - measured in hertz (Hz) the ___ the flux lines are cut at an angle, ___ flux lines cut per second, so less induced voltage as goes from 30 degrees to eventual 90 degrees the max lines cut

more, less

The induced voltage after 90 degrees of rotation is ___ -the voltage after 30 degrees of rotation will be ___ because the sine angle of 30 degree angle is 0.5 (100 x 0.5) = 50 volt

100 v, 50 volts

peak value or ___ - measure from zero to highest value in either positive or negative direction -the peak value is either positive or negative direction.

(amplitude)

- the peak value is one - half of the peak-to-peak value True or False

True

___ sine wave value of 100 volt cannot produce as much power as 100 volt of ___. (Since it increase to 100 volt but decrease to zero, equal time)

AC, DC

(actual AC value) RMS = peak x 0.707 peak = RMS x 1.414 (rating) - just use an ___ value of AC voltage that produce same power as of DC volt value

equal

AC (Trigonometry) Apparent power (VA) - the value found by multiplying the ___ by the ___ of an AC circuit. -apparent power - measured in volt-ampere (VA) & should not be confused with true power, measured in Watts. Watt (W) - a measure of true power

applied voltage, total current

Impedance (Z) - ___

the total opposition to current flow in an electrical circuit

Reactance - ____

the opposition to current flow in an AC circuit offered by pure inductance or pure capacitance

Resistance - the opposition to current flow in an AC or DC circuit

Average values - of voltage & current are actually ___ values - when sine wave of AC is changed into DC with rectifier. The average value produces the same amount of power as a non pulsating battery - source voltage (half-wave rectifier) average voltage - Efm x 0.637 = Eav (full-wave) then divide by 2 Eav / 2 = Eav (half-wave)

Wavelength (λ)(lambda) - ___

distance the radiating field or signal can travel during one cycle.

λ (wavelength) = speed of light (meter per sec) / frequency 300,000,000 m/s / 100,000,000 Hz

DC circuits have only one basic type of load (resistive) - true power - power in pure resistive AC circuits have watts (power)

Conductor Resistance (ohms) depends on: (3 things) 1. type of ___ (conductor is made of) 2. ___ (conductor) 3. ___ (conductor)

material, length, diameter

eddy currents from AC cause electrons to repel to outer surface of conductor (____) - ___ diameter, increase resistance

skin effect, decrease

A (quantity) = XL (inductive reactance) / R (resistance)

pure inductance (round wave) internal resistance (jagged wave)

Watts P (True power) = ER x IR AC inductance can only periods when current & voltage are both (+) or (-) Cannot use P = V drop x I P = E power of square / R P = I power of square x R

Total voltage for AC inductance must use vectors (inductive total voltage) ET = ER (resistive voltage) + EL (inductive voltage)

VARs (reactive power)= ___ power of square (reactive current) x ___ (inductive reactance) -quadrature power -Wattless power

IL, XL

VA (apparent power) = ___

ET x IT

Power Factor (PF) = True power (Watts) / apparent power (VA) PF = R (resistance) / Z (____) PF = P (Watts) / VA (____) PF = ER (voltage drop) / ET (____) * cannot use current because current is the same (series AC, inductive ohms)

impedance, apparent, total voltage

angle theta (θ) = angle of VA (apparent) = VAR (reactive) + Watts (true) cosθ = ___ To find angle 53 degrees which means current & voltage is 53 degree out of phase with each other. y = o = VAR (reactive) x= a = P (Watts) h = VA (apparent)

PF = Watts / VA

(Total current) IT = VA / ___ (Impedance) Z = ET/ __ (Power Factor) PF = WT / ___

ET, IT, VA