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Magnetic Field

One last point of clarification on the physics of electricity, and we'll be ready to start looking at practical aspects that arise from the underlying physics. But first, we need to understand electromagnetism.

The effect of a magnetic field is called magnetism. It's caused by rotating electrical charges; that is, electrons orbiting and "spinning" around a nucleus.

We can think of magnetism as a kind of magnification of electrical charges, caused by the angular momentum of electrons. A simple electric charge creates attraction or repulsion in all directions. A magnetic field is more complex, it has a three-dimensional polarity with a north/south:

Illustration of a bar magnet and it's magnetic field with lines leaving the magnet's north pole and returning to the magnet's south pole.

Magnetic north and south are arbitrary names just like positive and negative charge used to describe repulsion of like polarity and attraction of opposite polarity along an axis.

Magnetism in metals arises when enough electrons have a similar angular momentum to create a net magnetic domain. This can happen as part of the natural geological process of creation, or during production for manufactured magnets. A strong enough magnetic field can also induce a magnetic field in other metals, by pulling their electrons into a unified orbit.

A magnetic field can also be created electrically. A weak magnetic field is created when a current flows through a piece of straight wire, but if that wire is coiled, a much stronger magnetic field is created. In fact, a simple, yet effective magnet can be created with just a standard AA battery, a piece of coated wire, and a nail:

Illustration of a nail magnet: a battery connected to a wire that is wrapped around a nail to strengthen the magnetic field of the current flowing through the wire.


Just as a magnetic field arises from the electric charges, a magnetic field can induce current into a wire that enters the magnetic field.

As we'll explore later, induction is a powerful tool, and in fact, it's how most commercial electricity has traditionally been generated. Whether hydroelectric, coal, nuclear, or wind, a turbine attached to what is essentially a large electric motor (coils of wire surrounded by fixed magnets) is spun, causing those wires to rotate within the magnetic field, which causes a current through them.

Induction is also important for a host of other uses, including transforming high voltages into lower voltages by inducing a current into a wire that's coiled next to a higher voltage wire. We'll explore this more in the next part of the tutorial.

For further reading on magnetism, see:

Next - Part 1 Review