Publisher Summary This chapter helps learn the basic theory of electricity. It begins with the description of Ohm's law, which states that voltage equals current multiplied by resistance. This law is one of the best taught principles in school for the budding engineer or technician. All other rules are based on this foundation. Its fundamental fact is that resistance impedes current flow. This impedance creates a voltage drop across the resistor that is proportional to the amount of current flowing through it. The chapter considers two other types of impedance that can be found in a circuit: inductive reactance and capacitive reactance. Every wire, trace, component, or material in the circuit has these three components in it: resistance, inductance, and capacitance. There are two ways for components to be configured in a circuit: series and parallel. Series components line up one after another; parallel components are hooked up next to each other. The chapter also describes Thevenin's Theorem, which is based on the idea of using superposition to analyze a circuit. When one has two different variables affecting an equation, making it difficult to analyze, one can use the technique of superposition to solve the equation, if one is dealing with linear equations. Using Thevenin's Theorem allows one to reduce any circuit into a voltage divider. Finally, the chapter discusses two different types of current that are alternating current and direct current. These terms came into being to describe a couple of different modes of electricity. A firm understanding of these two modes helps one in all aspects of engineering.