Study Guide

Electricity and Magnetism

Electricity and Magnetism 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.

Electricity and Magnetism Resources

Games and Tools

Electric Field Hockey
More like normal hockey than field hockey, but with electric charge instead of missing teeth.

Charges and Fields
Electric fields may be invisible—but not for long. Visualize charge, fields, and potentials to your heart's content.

Circuit Construction Kit
If Lego had gone into consumer electronics, they might have made something like this.


Tesla vs. Faraday
Tesla coils generate large sparks of electricity; Faraday cages protect people from large sparks of electricity—remember what the electric field is inside a hollow conductor. The only appropriate music? AC/DC, of course. (Bonus points: Adam Savage does the robot.)

And One More Thing About Tesla
They Might be Giants on the man who may have been the coolest engineer to ever live.

Wires Are The Worst
What if all power transmission was wireless? The space underneath your desk would probably be a lot neater.

Zip 'n Snort
While the bit on magnetism and electricity is spot on, the coyote's grasp of basic mechanics concepts could use some work.


Aurora Borealis
Caused by the interaction of charged particles with Earth's atmosphere, auroras are stunning displays of the beauty of nature and perennial additions to desktop wallpaper folders around the world.

Lightning Strikes
One of the more impressive natural displays of electricity at work, lightning results from excess charge build up in clouds. Tens of thousands of amps are releases by each bolt (if only someone could figure out how to use it).

Electricity and You
Everything you could ever want to know about American electricity generation, courtesy of the U.S. Energy Information Administration.