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ac final > final > Flashcards

final Flashcards

1
Q

How does flux density affect magnetism

A

the more dense the magnetic lines of flux, the more magnetic field

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2
Q

difference between magnetic and polar north pole

A

on opposite sides of the earth, magnetic is in south

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3
Q

what direction does flux flow

A

north to south

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4
Q

what is magnetomotive force

A

causes flux in a magnetive circuit

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5
Q

what is an alteration

A

½ cycle of a sine wave

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6
Q

what is the period of a sine wave

A

time required for 1 cycle

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7
Q

what is a hertz

A

unit of measure for frequency

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8
Q

what is frequency

A

number of complete cycles that occur in 1 sec

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9
Q

what is the time for one cycle of a 300Hz sine wave

A

3.33mS 1 / 300

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10
Q

what is the formula to calculate frequency

A

f=1/t

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11
Q

when does the peak voltage of a sine wave occur

A

90 degrees

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12
Q

What is peak to peak voltage

A

90 and 270 degrees

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13
Q

what is root-mean-square voltage, and why is it used

A

RMS, makes AC voltage equivalent to DC voltage

.707xPv

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14
Q

whats the equation for RMS voltage

A

.707xPv (peak voltage)

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15
Q

handheld meters read what type of voltage

A

RMS

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16
Q

what is inductance

A

opposes a change in current

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17
Q

how is an inductor constructed

A

coils around a feral magnetic core

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18
Q

4 factors that determine the amount of voltage inducted in a moving conductor

A

strength, length, speed, angles

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19
Q

what is a henry

A

unit of measure for inductance

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20
Q

difference between a relay and a solenoid, and when are they used

A

solenoid does mechanical work

relays are electrical switch

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21
Q

how does the number of turns affect the inductance of a coil

A

more turns means more inductance

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22
Q

at what point does a sine wave reach half peak value

A

30 degrees

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23
Q

inductors oppose a change in _______

A

current

24
Q

when testing a coil with an ohmmeter, what type of reading should be expected

A

small amount of resistance at first

25
Q

calculate total inductance in series

A

add them up

26
Q

calculate total inductance in parallel

A

resipical

27
Q

equation for time constant for LR circuit

A

t=L/R

28
Q

equation for time constant for CR circuit

A

t=RxC

29
Q

unit for measure that uses L

A

inductor; same as resistance

30
Q

unit for measure that uses capacitance

A

farads

31
Q

time constance that are required to achieve maximum current flow in an inductive circuit

A

5x

32
Q

what is the percentage for the first time constant, first discharge

A

63 percent

37 percent

33
Q

how is a capacitor constructed

A

2 metal plates separated by a dielectric

34
Q

compare how a capacitor stores energy compared to an inductor

A

Cap= electrostatic field

Induct=electromagnetic field

35
Q

what is the dc resistance of a normally operating capacitor

A

capacitors block DC

36
Q

how do u test a capacitor with an ohm meter and whats the results

A

volts? reads as an open circuit (OL)

37
Q

how does the size of the plates and the distance between the plates affect capacitance

A

bigger/closer the plates more capacitance, farther away more voltage

38
Q

what is the dielectric, and what type of resistance does it have

A

insulating material

infinite resistance

39
Q

calculate the total capacitance in series

A

resipical

40
Q

calculate the total capacitance in parallel

A

add them up

41
Q

capacitors oppose a change in_______

A

voltage

42
Q

what is a working voltage of a capacitor

A

peak amount of voltage it can use before breaking down

WV (working voltage)

43
Q

time constant formula for a RC circuit

A

t=RxC

44
Q

in a capacitive circuit the _____ leads the ______

A

current, voltage

45
Q

how many zener diodes are needed to make a bridge recifier

A

0 only diodes make a rectifier

46
Q

what is the difference between the primary and the secondary of a transformer

A

primary is the input voltage and secondary is the output voltage

47
Q

how does the winding ratio affect the voltage of the transformer

A

makes it a step up or step down transformer

48
Q

how does the winding ratio affect the power of the transformer

A

it does not effect it

P:in=P:out

49
Q

will a transformer work with a DC power source

A

NO

50
Q

compare a step down transformer to a step up transformer

A

step down, less voltage more current

step up, more voltage less current

51
Q

law of power with the regard to the primary and secondary of a transformer

A

P:in=P:out

power in equals power out

52
Q

calculate the secondary current flow for a step up transformer 1:5. secondary load is 220 ohm, primary voltage 120V

A

2.73A

53
Q

what is the value of a capacitor labeled 922

763

A

9200pf

76000pf

54
Q

what are the units of measurement for Xl,Xc,Z

A

ohms

55
Q

a series RL circuit has an impedance of 520 ohms at a phase angle of 42 degrees. what is the circuit resistance

A

386.44 ohms

56
Q

what are the 3 sides of the power factor triangle

draw and label where everything are on the triangle

A

VA, VARS, WATTS

57
Q

how is the power factor calculated

A

true/apparrent x 100 percent

ac final (1 decks)

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