Figure 50. Mica Capacitor Color Code

Electronic Principles
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a. Alternating Current (AC) and Direct Current (DC).

Alternating current is current which constantly changes in

amplitude, and which reverses direction at regular intervals.

Previously, we learned that direct current flows only in one

direction, and that the amplitude of current is determined by

the number of electrons flowing past a point in a circuit in one

second. If, for example, a coulomb of electrons moves past a

point in a wire in one second, and all the electrons are moving

in the same direction, the amplitude of direct current in the

wire is one ampere. Similarly, if half a coulomb of electrons

moves in one direction past a point in the wire in half a

second, then reverses direction, moving past the same point in

the opposite direction during the next halfsecond, a total of

one coulomb of electron passes the point in one second. The

amplitude of the alternating current is one ampere. The

preceding comparison of dc and ac is