ELECTRICITY, MAGNETISM, SOUND, AND LIGHT

SERIES CIRCUIT

In this unit you'll begin learning how to analyze circuits. Circuit analysis means looking at a schematic diagram for a circuit and computing the voltage, current, or power for any component in that circuit. Closely related to the task of circuit analysis is the task of troubleshooting, which means figuring out what is wrong in a circuit that is not working correctly. Analyzing and troubleshooting go hand in hand; when a circuit is not working correctly, the easiest way to figure out what's wrong is usually to measure voltages in the circuit and compare those measured values to the values that the voltages should have (which you compute by analyzing the circuit). The rest of this course will concentrate on analyzing and troubleshooting resistive circuits (circuits that contain only resistors in addition to power supplies). In later courses you'll learn how to analyze and troubleshoot circuits that contain other components, such as capacitors, inductors, diodes, and transistors. This unit covers just about everything you could ever want to know about the simplest type of circuit, which is called a series resistive circuit. Some of the things you'll learn here apply only to series resistive circuits, but other things apply to any kind of circuit. For instance, the rule called Kirchhoff's Voltage Law applies to all circuits, and is therefore a very important general rule of circuit analysis. First read entirely this article and attend short classroom discussion then work through the Self-Test questions below. Some Definitions

* First, we'll define some terms, it will be useful for us first to define the terms series connection and series path. And even before we define those terms, we'll define what we mean by saying that two components are connected to each other. * Defining these terms carefully will be a big help later when we get to more complicated series-parallel circuits. Connected Components

* Two components are said to have be connected to each other when there is a path of zero resistance joining a terminal of one component to a terminal of the other component. * Basically, this means that either the components are connected directly to each other, or there's a conductor (such as a wire, or a trace on a circuit board) that connects them together. * Examples: In the circuit shown below,

* VS is connected to R1 at one point;

* R2 and R3 are connected to each other at two points; * VS and R2 are not connected to each other.

Series Connection

* Now that we've defined what we mean by saying that two components are connected to each other, we can define what we mean by a series connection. * Two components are connected in series if they are connected to each other at exactly one point and no other component is connected to that point. * Notice that there are two halves to this definition, both of which must be met in order to have a series connection. 1. First, the components must be directly or indirectly connected at exactly one point, no more and no less. 2. Second, no other component can be connected to that point where the other two components meet. * The most common mistake that students make here is to remember the first half of the definition but forget about the second half. For example, in the circuit shown below, R1 and R2 are connected to each other at exactly one point, but the voltage source is also connected to that same point. Therefore, R1 and R2 are not connected in series.

Series-Connected Components Have the Same Current

* The most important property of series connections is that the current is the same in every series-connected component. * Example: In the circuit shown below, VS and R1 are connected in series, so we know that the current through VS must be the same as the current through R1. But R1 and R3 are not connected in series, so we cannot...