Unit 16 - Alternating Current
Phase differences are expressed in _____. sine waves phases Hertz degrees
degrees
When describing the relationship between voltage and current, the reference waveform is always _____. current resistance voltage none of these
voltage
_____ describes the steps necessary to determine the effective voltage or current value. Peak Root-mean-square Instantaneous none of these C
Root-mean-square
A simple ac generator consists of a loop of wire rotating across the lines of force between the opposite poles of a magnet. TRUE FALSE
TRUE
Alternating current is primarily used because it can be transmitted inexpensively. TRUE FALSE
TRUE
Effective ac voltage or effective ac current is the equivalent value of dc voltage or dc current that would produce the same amount of heat in a resistor. TRUE FALSE
TRUE
In ac generators that produce large quantities of electricity, the conductor coils are stationary and the magnetic field revolves within the coils. TRUE FALSE
TRUE
The movement of electrons themselves does not produce any useful work. It's the effects that the moving electrons have on the loads they flow through that are important. TRUE FALSE
TRUE
The rerm "phase" is used to indicate the time or degree relationship between two waveforms, such as voltage-to-current or voltage-to-voltage. TRUE FALSE
TRUE
The waveform for ac circuits displays the level and direction of the current and voltage for every instant of time for one full revolution of the rotor. TRUE FALSE
TRUE
When a magnetic field moves through a coil of wire, the lines of force of the magnetic field cause the electrons in the wire to flow in a specific direction. When the magnetic field moves in the opposite direction, electrons in the wire flow in the opposite direction. TRUE FALSE
TRUE
The output voltage of a generator depends upon the _____. number of turns of wire strength of the magnetic field speed at which the coil rotates all of these
all of these
In a purely resistive ac circuit, the current and voltage are _____. This means that they both reach their zero and peak values at the same time. in-phase out-of-phase a or b none of these
in-phase
The _____ wave is a waveform that is symmetrical with positive above and negative below the zero reference level. nonsinusoidal nonsymmetrical sine any of these
sine
The peak value is equal to the effective value _____. times 0.707 times 1.41 divided by 2 times 0.58
times 1.41
The number of complete waveforms in one second is called the "frequency." Frequency is expressed as "_____" or "cycles per second." degrees a sine wave phase Hertz
Hertz
A three-phase generator has each of its windings out-of-phase with each other by _____. 90° 120° 180° 360°
120
Phase differences are expressed in degrees. One full waveform is equal to _____. 90° 120° 180° 360°
360
A waveform image is used to display the level and direction of current, but not voltage. TRUE FALSE
FALSE
_____ is the value of the voltage or current at a given moment of time. Peak Root-mean-square Effective Instantaneous
Instantaneous
_____ is the maximum value that ac current or voltage reaches, both for positive and negative polarity. Peak Root-mean-square Instantaneous none of these
Peak
When the current waveform finishes before the voltage waveform, the voltage "_____" the current waveform. leads lags is in-phase with none of these
lags
If the voltage waveform finishes before the current waveform, the voltage is said to "_____" the current waveform. lead lag be in-phase with none of these
lead
A nonsinusoidal waveform is created when _____ loads distort the voltage and current sine wave. linear resistive inductive nonlinear
nonlinear
The combination of alternating-current and direct-current waveforms results in a _____ waveform. nonsinusoidal nonsymmetrical sine any of these
nonsymmetrical
The effective value is equal to the peak value _____. times 0.707 times 1.41 divided by 1.41 times 0.58
times 0.707
