Читать книгу Electronics All-in-One For Dummies - Lowe Doug, Doug Lowe - Страница 13

In the previous section, I list several ideas most of us have about electricity based on everyday experience. But the reality of electricity is something very different. Chapter 2 of this minibook is devoted to a deeper look at the nature of electricity, but for the purposes of this chapter, I want to start by introducing you to three very basic concepts of electricity: namely, electric charge, electric current, and electric circuit.

 Electric charge refers to a fundamental property of matter that even physicists as smart as Neil deGrasse Tyson don’t totally understand. Suffice it to say that two of the tiny particles that make up atoms — protons and electrons — are the bearers of electric charge. There are two types of charge: positive and negative. Protons have positive charge, electrons have negative charge.Electric charge is one of the basic forces of nature that hold the universe together. Positive and negative charges are irresistibly attracted to each other. Thus, the attraction of negatively charged electrons to positively charged protons hold atoms together.If an atom has the same number of protons as it has electrons, the positive charge of the protons balances out the negative charge of the electrons, and the atom itself has no overall charge.However, if an atom loses one of its electrons, the atom will have an extra proton, which gives the atom a net positive charge. When an atom has a net positive charge, it goes looking for an electron to restore its balanced charge.Similarly, if an atom somehow picks up an extra electron, the atom has a net negative charge. When this happens, the atom goes looking for a way to get rid of the extra electron to once again restore balance. Okay, technically, atoms don’t really go “looking” for anything. They don’t have eyes, and they don’t have minds that are troubled when they’re short an electron or have a few too many. However, the natural attraction of negative to positive charges causes atoms that are short an electron to be attracted to atoms that are long an electron. When they find each other, something almost magic happens… . The atom with the extra electron gives its electron to the atom that’s missing an electron. Thus, the charge represented by the electron moves from one atom to another, which brings us to the second important concept …

 Electric current refers to the flow of the electric charge carried by electrons as they jump from atom to atom. Electric current is a very familiar concept: When you turn on a light switch, electric current flows from the switch through the wire to the light, and the room is instantly illuminated.Electric current flows more easily in some types of atoms than in others. Atoms that let current flow easily are called conductors, whereas atoms that don’t let current flow easily are called insulators.Electrical wires are made of both conductors and insulators, as illustrated in Figure 1-1. Inside the wire is a conductor, such as copper or aluminum. The conductor provides a channel for the electric current to flow through. Surrounding the conductor is an outer layer of insulator, such as plastic or rubber.The insulator serves two purposes. First, it prevents you from touching the wire when current is flowing, thus preventing you from being the recipient of a nasty shock. But just as importantly, the insulator prevents the conductor inside the wire from touching the conductor inside a nearby wire. If the conductors were allowed to touch, the result would be a short circuit, which brings us to the third important concept …

 An electric circuit is a closed loop made of conductors and other electrical elements through which electric current can flow. For example, Figure 1-2 shows a very simple electrical circuit that consists of three elements: a battery, a lamp, and an electrical wire that connects the two.The circuit shown in Figure 1-2 is, as I already said, very simple. Circuits can get much more complex, consisting of dozens, hundreds, or even thousands or millions of separate components, all connected with conductors in precisely orchestrated ways so that each component can do its bit to contribute to the overall purpose of the circuit. But all circuits must obey the basic principle of a closed loop. All circuits must create a closed loop that provides a complete path from the source of voltage (in this case, the battery) through the various components that make up the circuit (in this case, the lamp) and back to the source (again, the battery).

FIGURE 1-1: An insulated wire consists of a conductor surrounded by an insulator.

FIGURE 1-2: A simple electrical circuit consisting of a battery, a lamp, and some wire.