Part 1:  AC Voltages and Current

In the previous chapter, we discussed a number of different circuit configurations.  The primary focus was on finding ways to determine the current that flowed through them and the voltages that appeared across the circuit’s elements.  All of this was done with fixed voltages.  Nothing changed in the circuit with time.

As a practical matter, these types of circuits are, in general, not very useful — they don’t do very much.  There are of course exceptions, but most practical circuits process information in some way.  They transform the input to the circuit to an output based on the signals fed to them.  To do this, you must feed the circuit, for lack of a better phrase, information that it can process.

By varying the input voltage, we can communicate different values.  The magnitude of the voltage can be used represent some piece of information.  For instance, the position of lever, the sound of someones voice, an image, or any number of things can be represented by the way in which a voltage changes over time.  The circuit can then manipulate that information to produce the desired output.

This chapter introduces the concepts needed to deal with these types of signals.  The focus of this chapter is describe these types of voltages, it is not to investigate how they can be used in a circuit.