Electromagnet, the magnet that works when you want

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Before talking about electromagnets, let's talk about normal and "permanent" magnets like the ones you have on your refrigerator and that you probably played with as a kid.

You likely know that all magnets have two ends, usually marked "north” and "south," and that magnets attract things made of steel or iron.

And you probably know the fundamental law of all magnets: Opposites attract and equals repel. So, if you have two bar magnets with their ends marked "north" and "south," the north end of one magnet will attract the south end of the other. On the other hand, the north end of one magnet will repel the north end of the other (and similarly, south will repel south).

An electromagnet is the same way, except it is "temporary" ie, the magnetic field only exists when electric current is flowing. You start it by switching the on/off button.

The basic idea behind an electromagnet is extremely simple: By running electric current through a wire, you can create a magnetic field.

By using this simple principle, you can create all sorts of items, including motors, solenoids, read/write heads for hard disks and tape drives, speakers, and so on.

An electromagnet starts with a battery (or some other source of power) and a wire. What a battery produces is electrons.

If you look at a battery, say at a normal D cell from a flashlight, you can see that there are two ends, one marked plus (+) and the other marked minus (-). Electrons collect at the negative end of the
battery, and, if you let them, they will gladly flow to the positive end. The way you "let them" flow is with a wire. If you attach a wire directly between the positive and negative terminals of a D cell,
three things will happen:

Electrons will flow from the negative side of the battery to the positive side as fast as they can.
The battery will drain fairly quickly (a matter of several minutes). For that reason, it is generally not a good idea to connect the two terminals of a battery to one another directly. Normally, you connect some kind of load in the middle of the wire so the electrons can do useful work. The load might be a motor, a light bulb, a radio or whatever.
A small magnetic field is generated in the wire. It is this small magnetic field that is the basis of an electromagnet.

Source: website How Stuff Works