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Note:
All voltages and currents that we have
discussed so far have been of the DC variety. The next section will describe
the difference between AC and DC voltages.
DIRECT CURRENT
Direct current (DC) is the type of
current that is supplied by batteries. The electrical force exerted by
the battery is constant. This does not mean that it never changes, but
it is not constantly changing polarity. The "difference
of potential" (means the same as voltage) stays either positive or negative
with respect to its "reference" (usually designated as ground).
ALTERNATING CURRENT
Alternating current is different from
DC in that it "periodically" changes polarity.
"Periodically" in the United States is 120 times/second. This is 60 complete
cycles per second. I will go into more detail about different types of AC voltage
measurements later in this tutorial.
If you look at the diagram above you
will see that the DC voltage is constant. The AC voltage is continuously changing. Let's say that the voltage of "Z" is 10 volts DC. The AC waveform has a few points on it marked. The voltages at those points are listed below. Please understand that the voltages are only at that point in time. If the waveform voltage was measured with a volt meter, it would read approximately 10 volts AC. All voltages are referenced to the black line.
A. 11 volts
B. 2 volts
C. 5 volts
D. -5 volts
E. -13 volts
I will explain more about measuring AC voltage later in this tutorial.
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