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34 Cards in this Set
- Front
- Back
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Alternating current can be defined as current that varies in
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Amplitude and time
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Before a 120-volt dc source can be used to power a 12-volt load, the voltage must be reduced. What method can be used
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A step-down transformer placed in series with load
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Alternating current has replaced direct current in modern transmission systems because it has what advantage?
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AC can be readily stepped up or down
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A waveform is a graphic plot of what quantities
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Amplitude versus time
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What property surrounds a current-carrying conductor
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A magnetic field
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What describes the magnetic field surrounding a current-carrying conductor
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It is perpendicular to and equal along all parts of the conductor
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What factors determine(s) the intensity of a magnetic field surrounding a coil
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The amount of current flow through the coil
The type of core material The number of turns in the conductor |
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When you grasp a coil in your left hand with your thumb pointing in the direction of the north pole, your fingers will be wrapped around the coil in the direction of the
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Current flow
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The power consumed in a conductor in realigning the atoms which set up the magnetic field is known as what type of loss
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Hysteresis loss
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The magnetic field surrounding a straight conductor is (a) what shape, and (b) is in what position relative to the conductor
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(a) Linked oblong
(b) Perpendicular |
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Why is a two-pole magnetic field set up around a coil
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Because separate lines of magnetic force link and combine their effects
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When a conductor is moving parallel to magnetic lines of force, (a) what relative number of magnetic lines are cut, and (b) what relative value of emf is induced
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(a) Maximum
(b) Maximum |
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When the induced voltage in a conductor rotating in a magnetic field is plotted against the degrees of rotation, the plot will take what shape
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A sine curve
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When a loop of wire is rotated through 360 degrees in a magnetic field, the induced voltage will be zero at which of the following points
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180 degrees
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When a loop of wire is rotated 360 degrees in a magnetic field, at what points will the induced voltage reach its maximum (a) positive, and (b) negative values
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(a) 90 degrees
(b) 270 degrees |
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When a coil of wire makes eight complete revolutions through a single magnetic field, (a) what total number of alternations of voltage will be generated and, (b) what total number of cycles of ac will be generated
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(a) 16
(b) 8 |
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According to the left-hand rule for generators, when your thumb points in the direction of rotation, your (a) forefinger and (b) your middle finger will indicate the relative directions of what quantities
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(a) Current
(b) Magnetic flux, north to south |
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Continuous rotation of a conductor through magnetic lines of force will produce what type of (a) voltage and (b) waveform
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(a) AC
(b) Sine wave |
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What is the term for the number of complete cycles of ac produced in one second
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Frequency
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What is the unit of measurement of frequency
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Hertz
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A loop of wire rotating at 60rpm in a magnetic field will produce an ac voltage of what frequency
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360 Hz
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An AC voltage of 250 Hz has a period of
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0.004 second
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What is the approximate frequency of an AC voltage that has a period of 0.0006 second
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1667 Hz
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An AC voltage has a frequency of 350 Hz. In two seconds, what total number of times will the peak value of voltage be generated
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350 times
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The value of current of an AC waveform taken at any particular moment of time is what type of value
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Instantaneous value
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While the value of an AC voltage may be expressed as one of several values, the accepted practice is to express it as what type of value
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Effective value
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The total of ten instantaneous values of an alternation divided by ten is equal to what value
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The average value
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What mathematical formula is used to find the average value of voltage for an AC voltage
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Eavg = 0.636 x Emax
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The value of alternating current that will heat a resistor to the same temperature as an equal value of direct current is known as
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Ieff
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The rms value for an AC voltage is equal to what other AC value
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Emax
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What value will result by squaring all values for Einst, averaging these values, and then taking the square root of that average
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Eeff
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An AC voltmeter is usually calibrated to read which of the following AC values
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Peak-to-peak
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If the maximum value for an AC voltage is known, the Eeff can be found by using what formula
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Eeff = Emax x.707
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What is an important rule to remember when using Ohm's Law to solve AC circuit problems
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Never mix values
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