Sections 2.1-2.3 and 5.2 in Matter and Interactions (4th edition)

Magnetic Forces in the Real World

In this set of notes we will be defining the push or pull produced by a magnetic field (maybe not surprisingly) as the magnetic force. We will continue to look at the most simple case - the force from a magnetic field on a single moving charge, before moving on to consider more complicated situations like a current carrying wire. It turns out that the most complicated case with regards to magnetic forces is actually how one bar magnet attracts another, requiring torques and something we call the magnetic moment. This may be covered in your future courses, but for our purposes we will stick with the magnetic force on a moving charge (or eventually the force on a wire).

In the real world, the magnetic force is actually extremely relevant and has wide-spread applications. For example, the mass spectrometer is largely based on the magnetic force and allows scientists (of all varieties) to distinguish/separate particles that have different masses. In addition, the reason why both the Aurora Borealis and Aurora Australis occur at the poles of the Earth and not in between has to do with the shape of Earth's magnetic field and the force it exerts on charged particles coming from the sun. (This also why you may hear that the Earth's magnetic field acts as a “shield”.) The magnetic force can also be used to create an electric motor or a rail gun or levitate a frog.

Important Points to Remember about Forces

The magnetic force is simply a force like any other kind of force (i.e. gravitational force, spring force, or electric force). As such, we already know that the magnetic force:

In the next pages of notes, we will go over in detail how to find the magnetic force on a moving charge.