Electrical Circuit

Oct 11, 1996

RAY: We all know when you get into the car to start it, you put the key into the ignition, and you turn the key and electricity is directed by doing that: from the battery to the starter motor. And, of course, it makes a complete path and goes back to the battery. In fact, electrons make their migration from the negative end of the battery, into the starter motor and then back into the battery. That's how the flow of electricity takes place from the negative to the starter to the battery. Now, knowing that, if an electron were to start out at the negative terminal of the battery and you have 10 feet of battery cables and the starter motor -

TOM: Like 5 feet to the starter motor and 5 feet back.

RAY: No, I was thinking more like 4 feet to the starter and 6 feet back. How long then does it take a single electron starting at the negative battery terminal to reach the positive terminal? That is, to make the whole so-called circuit. Now, I could make this a multiple choice question, but I'm going to leave it open-ended.

TOM: Sure. I like open-ended because now, it leaves itself open to right-brained-type answers and essay-type answers.


RAY: Now you'll notice I didn't mention how much wire was inside the starter motor.

TOM: Like it almost doesn't matter.

RAY: Right. It doesn't matter. Let's say you say 10 feet over 5,280 feet. That's 1/500th of a mile. Right? And electricity travels at 186,000 miles per second, using the formula distance equals rate times... you could figure it out right? A simple calculation that any moron could do.

TOM: And many did.

RAY: Did you do it?

TOM: Yea. I even used my slide rule. I got slide rule accuracy with it.

RAY: And you'd come up with some answer.

TOM: I got a number and I didn't know where to put the decimal point. But I know what the answer is.

RAY: But the answer, amazingly is, about 4 hours.

TOM: Oh. Come on!

RAY: Because electricity is indeed the flow of electrons. Most electrons are bumping into other ones and pushing stuff around. It's sort of like having billiard balls in the air. What's happening is the energy is flowing through the wire, but the electrons, an individual electron, takes a long time because it is bumping into what?

TOM: Other electrons.

RAY: And atoms in the wires. So that's the answer.

TOM: How does one get four hours?

RAY: According to this brilliant electrical engineer. Whose name he wrote with invisible ink.

TOM: This is the most bogus puzzler.

RAY: I have a better one for this week.

TOM: I hope so.

Get the Car Talk Newsletter