TABLE OF CONTENTS Alternating current (AC) is the most naturally occurring form of energy in the universe. If you have a fair grasp of direct current (DC) then alternating current is a relatively easy concept. It is essential that you understand the behavior of alternating current. Most of the modern world uses these behaviors to run industry, provide information, support medical therapies, the list of uses is endless. To understand AC is to understand the why of modern technology.
Alternating current (AC) is defined as an electrical current that changes amplitude continuously and periodically changes polarity. A little investigation will show that we have already discussed most of the concepts of AC. For example, it still obeys Ohm's Law (for the instantaneous amplitude and polarity it exhibits at any selected moment).
Understanding alternating current only requires a modification of what you've already learned. The following explanation, though simplistic, it is also quite true: we can simulate AC by a switched or square wave and this will meet our definition for changing amplitude and periodically changing phase.
Figure 9-1 is an illustration of the procedure for mechanically generating a form of AC using two batteries and a switch. The wave-form is the voltage across the resistor as a result of the present switch condition plus each switch condition prior to this condition, so there is history in the wave-form (in all wave-forms). The wave-form is a graphic (or actually, a graph) of the voltage across the resistor...
