Resistors, capacitors, and inductors are the basic components that make up electrical circuits. For each, we will give a formula that relates voltage and current that is based on an underlying physical law. We will see what happens when we apply a voltage or current source to circuits with these components. In addition, we consider circuits with a semiconductor device, the diode. Analyzing circuits requires a lot of algebra. The expressions get so complicated that it is difficult to see what is going on. For this reason, it is important to express the results in a simple form that can be understood, and it is worthwhile to try different approaches to find the simplest path to a solution and to make sure that you understand it.