Magnetic Field Principles

Discussion of Principles

Permanent Magnets

Permanent magnets are dipoles and thus always have two poles: North and South. A compass is a small permanent magnet that is allowed to orient itself in the Earth's permanent magnetic field.

The magnetic force between magnetic poles acts according to: like poles repel, unlike poles attract.

Obviously, the geographic north pole of the Earth is the Earth's south magnetic pole.

Magnetic Fields and Magnetic Field Lines

The direction of the magnetic field at a point is given by the direction of a tiny compass needle placed at that point. Magnetic field lines are drawn so that the tangent points in the direction of the magnetic field at every point. Note that they must have a direction to allow the proper tangent to be chosen.

Faraday's Law and Lenz's Law

Faraday's law states that a changing magnetic flux through a loop will induce an emf within the loop.

Lenz's law states that this emf will always act to produce currents that tend to oppose the change in flux.