DC Electrics - Basic Principles — Page 1, Lesson 11

Alright, let's start right at the beginning of DC Electrics. I want to walk you through the basic principles that everything else in aircraft electrical systems is built on. First, we need to understand what an electric current actually is. An electric current is created when electrons are caused to move through a conductor. That's the core idea: moving electrons explain most electrical effects we deal with. Now, to understand electrons, we have to look at what everything is made of. All materials consist of tiny particles called atoms. An atom is made up of a nucleus and electrons. The electrons orbit the nucleus, kind of like planets spinning around the sun. Different materials have different numbers of electrons. Here's the key part about charge. Electrons have a negative charge. The nucleus has an equal number of positive charges, which are called protons. Because the number of negative electrons equals the number of positive protons, the atom as a whole is electrically neutral. The negative electron is held in its orbit by its attraction to the positive nucleus. But not all electrons are held equally tightly. Electrons in the outer orbits are not so strongly attracted to the positive nucleus. These outer electrons may easily fly off and attach themselves to a neighbouring atom in the material. These are called free electrons. Let's look at what happens when an atom gains or loses an electron. An atom that has lost an electron becomes more positive and is called a positive ion. An atom that has gained an electron becomes more negative and is called a negative ion. So if we can make those free electrons move in a particular direction through the material, we have created an electric current. This leads us to two fundamental categories of materials. Materials which have free electrons are called conductors. Examples are copper, silver, and aluminium. Materials which have very few free electrons are called insulators. Examples are wood, rubber, glass, and plastics. So how do we actually cause electrons to move along a piece of wire? We do it by applying a positive charge from some source at one end of the wire and a negative charge at the other end. The positive charge attracts the free electrons, and the negative charge repels them. This creates a flow of electrons in one direction through the wire, from the negative terminal to the positive terminal. Now, this is a critical point for maintaining a useful electrical system. To maintain the current flow, the force which caused the electrons to flow in the first place must be maintained. If that force stops, the electrons will all collect at the positive terminal and the current flow will cease. So to keep the current flowing, the source of that force must be sustained.