RfReduce.Com BLOG
Art: Magnetic Fields 2 
In a previous article we discussed the electromagnet that can be constructed from a nail, a coil of wire and a battery. Let's look at this a little more closely.

The is a current flowing in the coil of wire that wraps around the nail. A current is a flow of electrons. Any time there is a flow of electrons, there is a corresponding magnetic field around the wire, or whatever medium it is that is carrying the electric current. In the case of our electromagnet example, wrapping the wire around the nail as a coil-of-wire, is the most efficient way to get most of the magnetic field (of the wire) into the nail.

If the current in the wire is changing, then the magnetic field is changing. These two, the current and the magnetic field, are tied-together, so to speak.

So we have looked at how a flow of current (electrons) brings about a magnetic field. Let's look now at the opposite effect, that of a magnetic field, CAUSING a flow of current to occur.

Let's take a coil of wire and and connect the two ends of this coil to a small light bulb, like the bulb that is found in a small flashlight.

Now let us take a bar magnet and wave it around very close to the coil. We should see the light bulb flash a bit. We may have to turn off the room lights to see this if the bar magnet is not too strong.

What has happened is that the CHANGING magnetic field is inducing a current, a flow of electrons, in the coil. That current is lighting the light bulb. This is called, INDUCTION. The changing magnetic field (as we wave the bar magnet around) is INDUCING a current in the coil.

This is a most important concept to understand. A field (in this case a magnetic field), something that we cannot see, is causing a flow of electrons in some other device, circuit or system.

Now we have a FIRST PRINCIPLE on the idea of inducing currents into the human body. There are many sources of magnetic fields such as cell phones that can induce currents into the human body. In a subsequent article we will discuss how to prevent this from happening.