NOTE: This article was written quite awhile ago for the beginnings of what has become this web site. I sure was enthusiastic about coils then! This was at the time when I was discovering how to make a Tesla coil, probably just after I got mine working. In fact, I remember seeing the purple glow for the first time when I turned it on. Such an amazing thing.
This article was going to be followed by a part 2 which would get into detail about the workings of a Tesla coil. I never finished the second page. ASCII pictures only have so much appeal. If I do re-write this, it'll be with pretty graphics. If...
Anyway, I'm posting this in the hopes that someone will find it useful or informative. I'm not about to re-read it, but I think it covers on some concepts that took me awhile to figure out. Enjoy!
What a wonderful thing is a coil! Philosophies have said that time moves in a spiral--neither a circle nor a line, but a coil. The universe itself, I say, IS a coil. Radio transmitters and receivers, electromagnets, transformers, solenoids, inductors, ALL of these are simply coils of electricity with one difference or another.
In order to illustrate my enthusiasm for something as simple as a coil, let me discuss the basics of an electric current and coil, and the devices I have mentioned above.
Imagine a straight piece of wire with both terminals of a battery hooked to it. Try to visualize what is actually happening within the wire: Electrons from the battery flow from the NEGATIVE terminal to the POSITIVE terminal. Due to early misconceptions about electric currents, however, the idea that current from a power source flows from the POSITIVE terminal to the NEGATIVE terminal has always just stuck around. This is referred to as "conventional current".
If you have trouble getting yourself to say something that you know isn't true, then, here's something that might help. In real electron current, it's electrons doing the moving from one terminal to the other. In conventional current, something else moves. These are called "holes", essentially the spaces between electrons (whether they are a physical thing like electrons I don't know yet). Try this: Hold your hand flat on a table so that all your fingers are together. Now, move your pinky finger away from the other fingers. That makes a gap between it and your other fingers. Move your ring finger next to your pinky, and so on--the hole itself moves the opposite direction that your fingers are moving. So then think of current as the flow of holes from positive to negative--like bubbles floating to the surface in a tube of water.
Now then, any wire conducting an electric current gives a number of forces.
+ ----------------------> - (*conventional* current flowing L to R/+ to -)
One of these forces is a magnetic field, which is a circle centered over the wire, and exactly perpendicular (90 degrees) to the flow of electrons.
| |
-----|-----|----------->
| |
The vertical lines here represent this. The vertical magnetic field lines make a cylinder which surrounds the ENTIRE conducting wire, rather than just the two lines shown here. Remember also, if this wire was pointing at your eye, the vertical lines would look like circles around the wire:___ / \ | o | \___/That's about the best I can do with ASCII-art. The wire (o) there is pointing directly at your eye, and the circle around it is the magnetic field.
This magnetic field does revolve around the wire or otherwise move, like the electric current flowing through the wire does. However, a regular magnetic compass put near the wire will align itself with the magnetic field lines (and perpendicular to the wire). Try it! Take any wire, hold it over a magnetic compass, and connect the ends to a battery. Watch what happens.
The field lines then, are facing a certain direction. This direction is always the same relative to the electric current. If this is confusing, try the "Right-hand rule":
Hold your right hand, thumb up, against the wire. The thumb should be pointing TOWARDS the negative side, and AWAY from the positive--or along the conventional current flow. Wrap your fingers around the wire. Now, your fingers point in the direction that the North end of the compass is attracted to!
If you forget which hand to use or where to point your thumb, then put your right hand at the POSITIVE side of the current (You could also try remembering, positive=red=right...), and your left at the NEGATIVE side, and point the thumbs together along the wire. All your fingers now give the direction of the magnetic field lines. The nice thing here is that the left hand shows REAL electron flow as well as the correct direction of the magnetic field lines.
So now with the right-hand rule in mind, we know that the magnetic field is oriented like:
| |
+ ----|-----|----------> -
| |
V V <--aligned downwards on THIS side of wire
___<
/ \
V| o |^
\___/
>
where the bottom picture shows the wire's negative end facing us, and the V's are pointing the direction of the magnetic fields.
So now we have a pretty weak little magnet as long as the battery remains connected. But we want a stronger one.
| |
+ ----|-----|----------> -
| |
V V
| |
+ ----|-----|----------> -
| |
V V
<___< < < ___<
V / \ / \ ^
V | o | | o |^
V \___/ \___/ ^
> > > > >
Well lookie here! TWO wires, side by side, now make the magnetic field just that much stronger. Notice now, all the little V's showing the direction of the magnetic field circle around BOTH wires.
This is great and all--we doubled the magnetic field, after all--, but to get a *really* strong magnet from a current like this, we'd need MANY wires. Cutting a whole bunch of little straight wires up and hooking each one to the terminals of a battery doesn't sound that enthusing to me. What about, if we somehow double the SAME piece of straight wire we've been using, so that the current goes the same direction in two parts of it.
Wait, isn't that a COIL??
Yes, that's it! Wrap our wire around a round object--a pencil, say, and THEN the current flows in the same direction in a spiral all the way up the wire
_ _ _ / \ / \ / \ \_/ \_/ \(a coil, more or less)
And NOW we've got MANY wires next to each other, each with a current flowing in the same direction. Which means that we've also got an incredibly strong magnetic field!
This is our coil. And electromagnet. And solenoid. And inductor...and radio transmitter/receiver...and...and..and!
Also see my links.htm page for more information.
This web page created January 25, 2000
by Ryan Weh
please do not reproduce anything found within these pages (or elsewhere, for that matter) without due credit!