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164 Cards in this Set
- Front
- Back
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Inductors always ----- a change in current
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oppose
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Each time that an AC generator completes one complete rotation it is called a -----
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cycle
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The measure of the # of cycles per second of the voltage produced by an AC generator is called the ----- and is measured in ----
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frequency
hertz |
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At degrees on the sinewave is the voltage equal to zero? max positive and negative?
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360 and 180
90 and 270 |
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What are the 4 forms of measurement of voltage and current associated with sine waves?
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peak
peak to peak rms average |
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The peak to peak value is equal to ----- the peak value.
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2 times
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Another name for the effective value is the ----- value
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RMS
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How is the peak voltage value measured?
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zero to the highest value
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Another name for the effective values is the ----
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RMS value
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Explain RMS or effective value. Why is it used?
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RMS means Root Mean Square and it is the average of all the sign wave values which can be compared to DC heating effect of the same value
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What is the formula to fine Erms?
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Erms = Epeak x .707
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The time required for one cycle is called the ----
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period
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What is the average AC voltage for a full cycle of a perfect sine wave?
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zero
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An AC voltage the will produce the same amount of power as a like value of DC voltage is called the ----
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RMS value
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What is skin effect?
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This causes current to flow near the surface, reducing the cross sectional effective area and increasing resistance
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What causes skin effect?
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eddy currents- voltage forcing current away from the center of the conductor
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Skin effect is ----- at high frequencies.
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greater
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Load are normally connected in ----- with the source and the resistance of the line is in ----- with the source.
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-parallel
-series |
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The source for mechanical motion supplied to a generator is referred to as the -----
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prime mover
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In order to induce electrical energy into a conductor or generator there must be 3 factors present:
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-conductor
-magnetic field -relative motion |
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Current flow through a source (battery, generator or alternator) is ----- polarity
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positive to negative
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The rotating armature of an AC generator is conneceted to its external circuit through ---- while a DC generator uses a ----- to make the connection.
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slip rings
commutator |
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AC generators are constructed in 2 basic styles and are described by referring to the rotating member. Name them.
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-revolving armature
-revolving field |
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A revolving armature AC generator has each slip ring connected to what component?
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the rotating windings
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A 4 pole generator will be supplying serveral loads that are designed for 60 Hz. At what speed does the generator need to be driven?
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120 x 60 / 4 = 1800 rpm
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The revolving field AC generator has the armature winding positioned around the generator housing. The name given to the armature in this case is called the -----
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stator
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The formula to find synchronous speed of a motor is:
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120 x hz / # poles
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A rotating field AC generator is connected to the DC voltage source through -----
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slip rings
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The DC voltage and current that is supplied to the field of a generator is called the ----- power.
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excitation
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One full revolution of a 4 pole generator will result in ---- cycles of output
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2
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Current and voltage in an AC resistive circuit are ---- phase
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in
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The effective value of AC voltage will produce the same amount of ---- as a like value of ----- voltage
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heat
dc |
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When an AC voltage is given, it is always the ----- value unless otherwise stated.
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RMS
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V peak to peak
V peak V eff (rms) V average |
-360 sine wave
-180 sine wave -peak x .707 -peak x .637 |
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A pure AC sine wave has an average of ----- volts because the amount above zero is ----- as much as the amount below zero
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zero
exactly |
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Counter Electromotive Force is sometimes called ----- and CEMF is ----- degrees oop witht he applied voltage.
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back EMF
180 |
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The unit of inductance is the ----- and is represented by the letter ----
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-Henry
-L |
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Iron core inductors cannot be used for high frequency applications because of ----- loss and ------ loss in the core material.
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eddy
hysteresis |
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The oppposition to current flow in an AC circuit caused by an inductor is called -----
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inductive reactance
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What is the symbol for inductive reactance?
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XL
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Inductive reactance is measured in -----
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ohms
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The reactance of an inductive circuit depends upon the ----- of the coil and the ----- of the circuit.
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inductance
frequency |
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What is the formula to calculate inductive reactance?
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XL = 2(3.14) x f x L
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As frequency increases, the inductive reactance -----
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increases
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Inductive reactance causes current to ----- the voltage by 90 degrees.
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lag
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What is the trick for finding sin, cosine and tangent?
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SOH (ops/hyp)
CAH (adj/hyp) TOA (ops/adj) |
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On vectors, the horizontal is the ----- value and the vertical is the ----- value
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x
y |
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A vectors x component is ---- and the function you use is ----
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horizontal
cosine |
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A vectors y component is ----- and the function you use is -----
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vertical
sin |
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Reactance in the induction of ---- that limits the ----- flow in a circuit.
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voltage
current |
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The total current limiting effect of an inductor is called ----- and is symbolized by the letter -----
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impedance
Z |
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Give the equation for determining the total impedance in an inductive and resistive circuit.
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Z = sq rt R2 + XL2
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VARs is equall to the current flowing though an inductive circuit time the voltage appled to the ----
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inductive part of the circuit
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The true power consumed by the circuit is consumed by the ----- of the circuit.
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resistance
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The ratio of a coil's inductive reactance to resistance is referred to as the coil's ------ factor.
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Quality (Q)
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In a circuit containing only inductance (not possible) what is the phase relationship between the current and the applied voltage?
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90 oop, current lagging
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Inductive reactance of a circuit is directly proportional to ----- and -----
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frequency and inductance
(XL = 2(3.14) x f x L |
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Impedance is measured in ----- and is designated by the letter -----
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ohms
Z |
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The ----- is a ratio of true power to apparent power.
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power factor
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Power factor is generally expressed as a -----
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percentage
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The angular displacement by which the voltage and current are oop with each other is called ----
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phase angle
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What is the physical structure of a capacitor?
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consists of 2 conducting surfaces referred to as plates separated by some type of insulating material called the dielectric
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The unit of capacitance is the ----- abbreviated -----
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farad
F |
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One microfarad in decimal form is -----
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.000001 (10 -6)
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One picofarad in decimal form is -----
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.000000000001 (10 -12)
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Name 3 factors that determine the capacitance of a capacitor?
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- area of plates
- distance between plates -type of dielectric used |
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When a DC source is connected to a capacitor, what happens?
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electrons will be removed from the side connected to the + polarity and accumulate on the - side of the capacitor
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Electrons can flow only during the period of time that a capacitor is either ----- or -----
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charging
discharging |
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Do electrons flow through a capacitor?
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no (except leakage)
electrons flow in and out, but not through |
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If a capacitor is subjected to a voltage in excess of that for which it is designed, what may happen?
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it may puncture or breakdown causing an arc through the dielectric (shorted)
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In a capacitive circuit the current will ---- the voltage by 90 degrees.
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lead
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What effect does the type of dielectric have on a capacitor?
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it effects the voltage rating
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A time constant is the amount of time required to charge a capacitor to ----- percent of the amount left to reach its full charge. How many time constants are required to reach full?
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63.2
5 |
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Give the equation to find the time constant for a resistive-capacitive circuit
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T = (R x C) x 5
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------ is the property associated with a capacitor that opposes the flow of AC current.
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Capacitive Reactance
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Give the formula for calculating capacitive reactance.
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XC = 1/2(3.14)fC
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If the frequency of a circuit is increased the capacitive reactance is -----
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decreased
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If the capacitance is decreased, the capacitive reactance is -----
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increased
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Current appears to flow through a capcitor beacue of the ----- and ----- of voltage and ----- of current.
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increase
decrease direction (polarity) |
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In a charged capacitor, the voltage across the plates of the capcitor opposes the -----
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source voltage
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List 3 jobs that a capacitor can perform in electrical work.
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- block DC, pass AC
- correct power factor problems in systems - set timing constants for oscillators |
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A charged capacitor has a voltage potential across it. the conductor with a deficiency of electrons is the ----- plate
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positive
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The flow of electrons though the insulating material of a capacitor is called ------
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leakage
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----- charge is the term used to describe the stationary charge that is stored in a capacitor.
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Electrostatic
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A capacitor that has a high level of current flow though its insulating material would be considered to have a -----
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weak dielectric
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A 120 VAC source is applied to a capacitor. The voltage rating on the capacitor would have to be a minimum of -----
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170 volts you must find peak (RMS x 1.41)
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Non-polarized capacitors can be used in either ---- or ----- circuits.
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AC
DC |
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Oil-filled capacitors are often used in -----
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motor circuits
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Capacitors charge at a ------ rate that they discharge.
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same
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Polarized capacitors are ---- type.
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DC
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What will happen if you apply reverse polarity to a polarized capacitor?
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it will break down and short out
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List 6 rules when handling capacitors.
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- power off
-cap disconnected -cap has no charge -observe proper polarity -never hand someone a charged capacitor -check voltage rating is higher than applied voltage |
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The total capacitance of series capacitors is calculated the same way as the total resistance of ------ resistors.
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parallel
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When you connect 2 identical capacitors in series, what is effectively done?
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total capacitance decreases, however total Xc increases (you have 2x the dielectric)
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A capacitor ----- DC and ----- AC current though a circuit
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blocks
passes |
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Formula to find Ct in a series circuit.
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1/ 1/C1 + 1/C2 + 1/C3 ...
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Formula to find Xc of a capacitor when C and f are known.
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Xc = 1/ 2(3.14)fC
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The total capacitance of parallel capacitors is calculated the same way as the total resistance of ----- resistors.
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series
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Formula to find Cr in a parallel circuit.
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Ct = C1 + C2 + C3 ...
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Formula to find Lt in series.
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Lt = L1 + L2 + L3 ...
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Formula to find Lt in parallel
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Lt = 1/ 1/L1 + 1/L2 + 1/L3 ...
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The total inductance of series and parallel inductors in a circuit is calculated the same way as the total ----- is calculated for series and parallel resistors in a circuit.
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resisntance
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A circuit that contains resistance and capacitance is called a -----
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RC circuit
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For a series RC circuit, the ----- must be the same through all parts of the circuit.
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current
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A circuit that contains resistance and capacitance is called a -----
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RC circuit
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When solving a series RC circuit, the ----- is the reference
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current
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For a series RC circuit, the ----- must be the same through all parts of the circuit.
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current
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A series circuit has a large Xc and small R. The power factor is close to ----- percent.
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0
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When solving a series RC circuit, the ----- is the reference
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current
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A series circuit has a large R and small Xc. The phase angle is close to ----- degrees
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0
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A series circuit has a large Xc and small R. The power factor is close to ----- percent.
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0
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When finding the total reactance of a RLC circuit, XL and XC ------ each other out.
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cancel (subtract biggest from smallest)
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A series circuit has a large R and small Xc. The phase angle is close to ----- degrees
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0
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In a series RL circuit the ------ is in phase and in parallel the ------ is in phase.
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current (voltage oop)
voltage (current oop) |
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When finding the total reactance of a RLC circuit, XL and XC ------ each other out.
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cancel (subtract biggest from smallest)
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The current thgouth the resistive branch of a parallel circuit is ------ oop with the current though the inductive branch
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90 degrees
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In a series RL circuit the ------ is in phase and in parallel the ------ is in phase.
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current (voltage oop)
voltage (current oop) |
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The current thgouth the resistive branch of a parallel circuit is ------ oop with the current though the inductive branch
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90 degrees
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IR and IL must be added ------ to find the total current.
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vectorially
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IR and IL must be added ------ to find the total current.
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vectorially
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The PF in a RL parallel circuit is the ratio of -----
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true power to apparent power
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The PF in a RL parallel circuit is the ratio of -----
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true power to apparent power
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A parallel RLC circuit has as least ----- branches
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3
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In parallel RLC circuits the ----- is the same and is ------ phases across all branches and is uses as the main ------ for calculations.
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voltage
in reference |
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The current and voltage relationship in a parallel RLC circuit is -----
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-resistive 0 phase angle in phase
-inductive 90 degrees lagging -capacitive 90 degrees leading |
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In a parallel circuit that contains both XL and XC, the reactive currents -----
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subtract
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Inductance and Capacitance are ------ oop from each other
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180
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----- occurs at a frequency when XL is equal to XC.
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Resonance
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A circuit having resitance, inductance and capacitance is sometimes known as a -----
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RLC tank
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What is the power factor of a circuit containing only Xc?
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0
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A series circuit has an XC greater than XL. The circuit is defined as being ----- and the line current will ----- the line voltage.
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capacitive
lead |
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Minimum impedance for a parallel RLC circuit is ----- and this occurs when the frequency is ----- or ------
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zero
zero undefined |
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---- is the angle of displacement between line current and line voltage.
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Phase angle (angle theta)
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Increasing the value of inductance in a parallel RLC circuit will cause the circuit to be more -----
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capacitive
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Increasing the value of capacitance in a series RLC circuit will cause the circuit to be more ------
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inductive
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Resonance is defined as the frequency where ----- is equal to -----
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XC
XL |
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At series resonance, the impedance of the circuit is equal to the ----- and the current is -----
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resistance
maximum |
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At resonance, the appled voltage and current are ----- and the power factor is ----- percent
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in phase
100 percent |
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The impedance of a RLC circuit in parallel at resonance is ------- and the current is ------
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maximum
minimum |
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The addition of resistance to a reactive series circuit always ----- the power factor of that circuit.
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increases
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Define power factor.
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The ratio of true power (resistive) to apparent power
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Poor power factor in a plant is normally caused by ----
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inductance
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Power factor is normally corrected by adding a ------ in parallel with the load.
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capacitor
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The greatest economies are when the capacitors (to correct PF) are placed ----
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at the load
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A three phase power source can be produced by rotating a magnetic field through -----
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3 sets of coils arranged 120 degrees apart
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Another name sometimes used to refer to the wye connection is the -----
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star connection
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For a ----- connected device, the line voltage is higher than the phase voltage by a factor of -----
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wye
1.73 |
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For a ----- connected device, the line voltage is equal to the phase voltage.
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delta
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For a ----- connected device, the line current is equal to ------ the phase current.
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delta
1.73 times |
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For a ----- connected device, the line current is equal to the phase current
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wye
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Fluorescent lamps are about ----- percent more efficient than incandescent lamps.
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400
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List the three primary and 3 secondary colors of light.
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-red, green, blue
-yellow, cyan, magenta |
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What colors of light are combined to create white light?
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The primaries
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What is CRI?
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Color Rendering Index (describes the quality of light from 0 to 100 (perfect))
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All white light sources can be evaluated by ------ and -----
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color temperature
CRI |
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Natural light is considered to have a CRI of ----
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100 (perfect)
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What is efficacy?
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measured in lumens per watt, efficacy is the energy efficiency of a light source
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A ----- starts and regulates power to a fluorescent lamp
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ballast
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What are the 2 broad categories that Fluorecent and HiD Ballast fall into?
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-Magnetic
-Electronic |
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What is a luminaire?
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a device that inclueds a lamp holder and the means of electrification and support
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What is a lighting fixture?
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luminaires that are permanently attached to buildings
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Dimmers control light levels by controlling the ----- to the lamp.
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power
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What is daylighting?
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the process of designing buildings to utilize natural light to its fullest
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The gross amount of light generated by a light source is measured in -----
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lumens
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