Electricity and Magnetism Introduction Introduction

Until this point, our study of physics has existed solidly in the realm of the, well, solid: things we could touch, drive, throw, roll, slide, drop, push, or, when all else failed, fire out of cannons. Electricity and magnetism are fundamentally different.

Electromagnetic forces exist everywhere and all around us, but are invisible and intangible. Yet it's electromagnetism that is behind almost every invention of the modern world, from light bulbs to iPads. It's the theory that makes smart phone apps possible (by describing the motion of electrons flying through wires) and allows you to send text messages (by explaining how a cell phone antenna can send data through the air).

The basic unit of electromagnetism is electric charge, which can be positive or negative. Like charges repel each other, while opposites attract. Every charge creates an electric field around it, which interacts with other charged objects—almost exactly the same way a large, heavy object (like the earth) can interact with a lighter object (a human) via its gravitational field. Just like the force of gravity has an associated potential energy, collections of charges have an electric potential associated with them.

Electrical engineers have figured out how to harness this potential to create circuits, or paths that use electrons to do work. This electron action powers your dishwasher and touch screen. Without circuits, we couldn't scroll through our Instagram pics. That's enough to make us want to stop and hug an electrical engineer.

Moving charges create magnetic fields—electricity and magnetism are really two sides of the same bar magnet. Just like electricity, magnetism has polarity, labeled north and south, and opposite poles attract.

Unlike electricity, however, there is no way to isolate a magnetic pole. Break a refrigerator magnet in half and you're left with two smaller refrigerator magnets (don't try this with the refrigerator itself). The interaction of electricity and magnetism, called electromagnetic induction, can be used to generate power, turn motors, accelerate particles, and is an essential part of our modern lifestyle.

In this chapter, we'll cover the basic principles of both electricity and magnetism. We'll also explain how scientists and engineers have harnessed electromagnetism to create some of the everyday devices we know and love. Or hate. It depends how you feel about office printers.