Ask a Physicist: The Speed of Electricity

Last week, a reader named Nabilah wrote in to ask: Electrons carry charge, but I've been told that electrons in a DC circuit actually move slower than a snail, and in an AC circuit, they don't move at all, just shifting to and fro. Then how does that make a lightbulb light up? Nabilah,What you've been told is correct, but I can see how it'd be confusing--after all, when you hit the light switch, the lights come on instantly! So let's explore what's going on here.First off, it's crucial to unders...