Lecture Text.
AC Circuits.
Many of the principles discussed in the DC lectures still apply to AC circuits.
The new factor presented with AC circuits are that voltage periodically reverses
polarity, producing a reversing current. More importantly these
voltages and currents are constantly changing. They are usually expressed
mathematically as sinusoidal or exponential functions.
One
advantage of AC power is that its voltage level can be stepped up or down with
transformers. Transmission of AC power occurs at very high
voltage (over 100,000 volts) for very long distances. AC power is
generated at 60 Hz (in the United States), 50 Hz (in Europe ) and 400hz
(Military). Power distribution is the province of electrical engineers,
and electricians. Electronic circuits use both DC and AC signals ranging
generally from audio to microwaves.
Passive electronic circuits are combinations of resistors,
inductors, and capacitors. Associated with resistors, inductors, and
capacitors are resistance, inductive reactance, and capacitance reactance, respectively.
The resistance of a resistor is a property of the resistor. It effects AC
the same as DC. Capacitors block DC current or appear as an open in DC
circuits. Air gap capacitors read just like a open with an ohm-meter.
Other types will be discussed later. Inductors are essentially short
circuits in DC circuits. Inductors are coils of wire so that they actually
do have the resistance of the wire. The wire used is usually copper for
low resistance and ease of coiling.
The impedance of a resistor is
simply the resistance of the resistor and is the same for all frequencies.
The capacitance reactance of a circuit is a function of frequency.
Capacitance reactance is a inversely proportional to frequency. The higher the
frequency the less the capacitive reactance. The impedance of an inductor is
proportional to signal frequency and is referred to a the inductive
reactance.
For a thorough analysis of AC
principles you click on links below. This subject is covered in most basic
electronics or physics books that you can get at your public
library. AC circuits are relatively complex. High school
algebra, geometry, trigonometry and physics teach most of what is needed to
understand AC electronics.
