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My Electrical Foundation > Alternating Current > Flashcards

Alternating Current Flashcards

1
Q

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

A

faster

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2
Q

Induced voltage at 45 degree angle is ___

A

70.7 volts

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3
Q

RMS = actual ___ value

A

AC

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4
Q

Skin effect in AC circuits

frequency goes ___, skin effect goes ___

Large CMA, Resistance goes ___

A

up, up

down

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5
Q

Skin effect = ___

A

tendency of electrons to move towards outside of conductor

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6
Q

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

A

same

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7
Q

resistive loads - contain pure ____

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

A

resistance, phase

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8
Q

___ circuit - electrons travel through entire conductor

___ circuit - electrons forced outside conductor (skin effect)

A

DC, AC

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9
Q

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

A

polarity

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10
Q

Inductive capacitance - ___

Impedance - ___

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

A

farads, ohms, XL

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11
Q

XL (inductive reactance) = ___

A

2 pie f length

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12
Q

Each is 63.5 (5 of them)

100 - 63.5 = 36.8

A
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13
Q

Inductance in AC circuits

____ = AC load, usually with coil

  • motors, transformers, lightning ballast, and chokes
A

Inductance (L)

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14
Q

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 ___

A

opposite, rate, current

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15
Q

Voltage goes up, current change goes up

True or False

A

True

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16
Q

An inductor opposes a change of current

True or False

A

True

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17
Q

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)

A

180

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18
Q

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

A
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19
Q

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

A

Z ,X, R

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20
Q

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

A

VA, VARS, Watts

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21
Q

____ = 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

A

0.637, 0.707,, 0.5

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22
Q

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

A
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23
Q

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)

A
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24
Q

60 cycles per 1 sec = 60 Hz

A
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25
Q

oscilloscope = see ripple voltages add

A
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26
Q

Magnetic Induction

____ = rate of certain occurences.

current rise 63.2 percent each time constant (5 times constant)

A

Exponential curve

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27
Q

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

A
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28
Q

Induced voltage spike

voltage spike - current flow stops and decrease.
- suppressed by ___ (MOV)

Diode = permits current flow in only one direction

A

Metal Oxide Varistor

29
Q

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
A

magnetic field, current

30
Q

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

A

Inductors

31
Q

Vertical = 180 degrees and 360 degrees

Flat (parallel) = 270 degrees and 90 degrees

shunt - field pole coil

A
32
Q

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

A
33
Q

Solenoid = converts energy (____) to ____

uses relay

A

(electrical), mechanical

34
Q

Impedance (ohms) =(inductive and capacitance)

A
35
Q

Hz = (# poles x RPM) / 120

A
36
Q

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

A
37
Q

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)
A

2 pie f L

38
Q

Terms (symbol) (unit)

Reactance (X) (ohms)
Inductance (L) H)
capacitance (C) (F)

Inductive reactance (XL) (ohms)
Capacitive reactance (XC) (Farads)
Impedance (Z) (ohms)

A
39
Q

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

A
40
Q

Wave forms (3 of them)

(Sine Wave, Square Waves, and Triangle waves)

A
41
Q

Oscillators = produce Square waves

A
42
Q

___ = a triangle wave

(voltage rise at a constant rate with respect to time)

A

linear wave

43
Q

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

A

more, less

44
Q

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

A

100 v, 50 volts

45
Q

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

A

(amplitude)

46
Q
  • the peak value is one - half of the peak-to-peak value

True or False

A

True

47
Q

___ 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)

A

AC, DC

48
Q

(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

A

equal

49
Q

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

A

applied voltage, total current

50
Q

Impedance (Z) - ___

A

the total opposition to current flow in an electrical circuit

51
Q

Reactance - ____

A

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

52
Q

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

A
53
Q

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)

A

DC

54
Q

Wavelength (λ)(lambda) - ___

A

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

55
Q

λ (wavelength) = speed of light (meter per sec) / frequency

300,000,000 m/s / 100,000,000 Hz

A
56
Q

DC circuits have only one basic type of load (resistive) - true power

  • power in pure resistive AC circuits have watts (power)
A
57
Q

Conductor Resistance (ohms) depends on: (3 things)

  1. type of ___ (conductor is made of)
  2. ___ (conductor)
  3. ___ (conductor)
A

material, length, diameter

58
Q

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

A

skin effect, decrease

59
Q

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

A
60
Q

pure inductance (round wave)

internal resistance (jagged wave)

A
61
Q

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

A
62
Q

Total voltage for AC inductance must use vectors

(inductive total voltage) ET = ER (resistive voltage) + EL (inductive voltage)

A
63
Q

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

A

IL, XL

64
Q

VA (apparent power) = ___

A

ET x IT

65
Q

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)
A

impedance, apparent, total voltage

66
Q

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)

A

PF = Watts / VA

67
Q

(Total current) IT = VA / ___

(Impedance) Z = ET/ __

(Power Factor) PF = WT / ___

A

ET, IT, VA

68
Q
A

My Electrical Foundation (15 decks)

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