Movement of Free Electrons

Free electrons are necessary for electrical current, but for the free electrons to move easily, they need two things—a complete pathway, or circuit, and a force that makes them move. The force from a battery can cause electrons to move. Like charges repel, so the negative electrons repel each other and are forced from the negative terminal of the battery. Unlike charges attract, so the electrons are attracted toward the positive protons in the positive side of the battery. In this case, free electrons flow in one direction only. This is called direct current. Most, but not all, circuits in passenger vehicles operate on direct current. The larger the charge between the negative and the positive terminal, the more strongly the positive terminal attracts and the negative terminal repels the free electrons. This attraction/repelling acts as a force driving the electrons along. The greater the force, the stronger the electrical current. The force is called electromotive force, and it is also referred to as voltage. So you could say that voltage is the force that motivates electrons to move and is measured in volts.

Technician Tip
Since electrical current is the flow of electrons, it is natural to say that the direction of current is the direction in which the free electrons move—from negative to positive—which is called the electron theory. However, before the discovery that they are negatively charged, it was thought the natural way for electrons to flow was from positive to negative, which is called the conventional theory. Most wiring diagrams are written from the conventional theory perspective, while electronic circuits are typically designed and operate on the electron theory perspective. Thus, both concepts are still in use. In fact, a third theory exists that closely mirrors the conventional theory, called the hole theory. It states that while negative electrons do move from negative to positive, holes move from positive to negative as electrons move from atom to atom; in this case, holes (current) flow from positive to negative, and are sometimes called “positive holes.” What’s most important to remember is that voltage causes current to flow through conductive paths (resistance). We will be using the conventional and hole theories when explaining the electrical concepts throughout this text unless otherwise noted.