Physics Van 3-site Navigational Menu

Physics Van Navigational Menu

Q & A: How electrical circuits work

Learn more physics!

Most recent answer: 10/22/2007
Q:
We want to know how electrical circuits work. And we want to know what is the connection between electricity and magnets?
- NICKIE AND FELIX
NEW YORK, NY
A:
Nickie and Felix,

I'm not sure how old you are, so if this answer doesn't make sense, please write again.

Connection between electricity and magnets

Good question! This is the kind of thing that scientists think about all the time. It's great that you wonder about how things are connected to each other!

First let's just think about electric charge. There are positive charges and negative charges. If two things have the same charge they'll push away from each other, but if they have opposite charge they'll pull toward each other. Physicists usually talk about this by saying that charged things produce a positive or a negative electric field, and that this electric field pushes or pulls other charged things. Don't worry about exactly what an electric field is, but just like your ears notice the sound from a speaker, and your eyes notice the light from a light-bulb, charged objects notice electric fields. Basically, the electric field is just a fancy way of saying that a charged object produces something that will push or pull anything charged that comes along. So, if you have a bunch of charged objects near each other, they'll all produce electric fields and at the same time, each of the objects will feel pushes and pulls from the electric fields of all the other charged objects!!

Now for the connection between electricity and magnets. We just talked about charges making electric fields, and also that charged things feel pushes or pulls from electric fields. But those charged things were sitting still! When charged things move, they produce another kind of field that will push or pull any other charged thing that is moving. This is called a magnetic field. It can get a little confusing, but if you have a bunch of charged objects, then the ones that are moving will produce magnetic fields, and those objects will also get pushed and pulled by the magnetic fields made by the other charged things that are moving. This is just like what happened with the electric field, except that instead of talking about charged things pushing on other charged things, now we're talking about moving-charged things pushing on other moving-charged things.

By the way, moving charges still produce electric fields and feel pushes and pulls from other electric fields. So, now our group of charged things that are moving around is feeling both kinds of pushes and pulls (electric and magnetic).

So, if it takes moving charges to make a magnet, does that mean that those ordinary magnets (like refrigerator magnets) have moving charges in them? Yes!! The molecules in the atoms of the magnet are made of charged particles, and those charged particles are moving around!

OK, now to your question about how electric circuits work.

Basically, an electric circuit is an obstacle course for electrons. Electrons are extremely small charged objects (much too small to see even under a microscope). To make a circuit, you need paths for the electrons to follow, and a power-source to push them along. Electrons travel very well through metal things. So, in a circuit, the paths are made of thin pieces of metal (wire!). A power source for the circuit would be something like a plug in your house, or a battery.

A simple circuit would be a light-bulb connected by two wires to a battery. First, the electrons get pushed out of the battery (because of an electric field just like in your first question!). Then they pass through the light-bulb, and then back to the other side of the battery. When they pass through the wire in the light-bulb, they make it so hot that it glows brightly enough to light a room!

Now, you can get much more complicated circuits than that. For example, TV's and computers and all the other modern electronics have incredibly complicated courses for the electrons to follow. And along the way, the energy in the electrons is used to do all kinds of cool things.... like doing all the things a computer can do... but that's another question!

Truly, the electrons don't really go racing all the way along the wire paths. They actually just keep pushing each other along like millions of little balls in a line that keep knocking each other forward. So, if the electrons in your computer aren't following the course that the computer-maker wanted them to follow, your computer won't work correctly. That could either be because the path has been damaged, or it could be because the computer-maker made a little mistake in designing the paths for the electrons in the first place :).

-JAE

(published on 10/22/2007)

Follow-up on this answer.