An electric circuit is the combination of any number of sources and loads
connected in any manner which allows charge to flow. The electric circuit
may be simple, such as a circuit consisting of a battery and a light bulb. Or
the circuit may be very complex, such as the circuits contained within a television
set, microwave oven, or computer. However, no matter how complicated,
each circuit follows fairly simple rules in a predictable manner. Once
these rules are understood, any circuit may be analyzed to determine the
operation under various conditions.
All electric circuits obtain their energy either from a direct current (dc)
source or from an alternating current (ac) source. In the next few chapters,
we examine the operation of circuits supplied by dc sources. Although ac
circuits have fundamental differences when compared with dc circuits, the
laws, theorems, and rules that you learn in dc circuits apply directly to ac
circuits as well.