Welcome to Chapter 16 — AC Electrics and Semiconductors — Page 249, Lesson 266

Welcome to Chapter 16 — AC Electrics and Semiconductors. This is a fresh topic, so let's start from the ground up. I want to walk you through what semiconductors are and why they matter to you as a pilot. The chapter opens by reminding us that most people own a calculator, and that even a simple one has more computing power than the systems that took Neil Armstrong to the moon. That's a striking comparison, but the key point is this: transistorization and miniaturization have allowed us to build ever more sophisticated electronics and package them in ever smaller units. As a modern pilot, you rely heavily on the electronic flight systems incorporated in your aircraft. That means you must have an understanding of how transistors — or more specifically, semiconductors — work. Before we dive into semiconductors themselves, we need to remind ourselves about the general atomic construction of conductors and insulators. Let's start with the simplest atom: the hydrogen atom. A hydrogen atom consists of a nucleus containing one proton, which is positively charged, and one neutron, which is neutrally charged. Orbiting around that nucleus is one electron, which is negatively charged. Conductors and insulators have more complex atoms. They have an increasing number of neutrons, protons, and electrons — and importantly, the numbers of protons and electrons are equal, so the atom is electrically neutral overall. The electrons orbit the nucleus in multiple orbits, or shells. These atoms are held together by bonds formed between the valence electrons — that's the electrons in the outermost shells. The atoms arrange themselves into a lattice-type arrangement, meaning they are equidistant from each other in a regular pattern. Now here's the critical distinction: electrons in the outer shells are less tightly bonded to their parent atom than those in the inner shells. Because of that, they are free to move from one atom to the next. These electrons are known as free electrons, and they form the basis for current flow within the material. So to summarise what we've covered so far: we have the hydrogen atom as the simplest model, with one proton, one neutron, and one electron. Conductors and insulators have more complex atoms with multiple shells. The outer-shell electrons, called valence electrons, are less tightly bound and can become free electrons. Those free electrons are what allow current to flow. This sets the stage for understanding how semiconductors differ from conductors and insulators, which we'll get into next.