# Chapter 18: Magnetism

Difficulty Level: At Grade Created by: CK-12

We are familiar with magnets mostly as devices to stick to a refrigerator, or perhaps as the inner working of a compass.  Magnetic fields really are related to electricity.  A permanent magnet like a refrigerator magnet or a compass needle creates a magnetic field from the inner motion of its electrons.  However, any moving charge can create a magnetic field, however, small.

Chapter Outline

### Chapter Summary

1. The magnitude of the force on a straight current-carrying wire within a magnetic field is given by the equation \begin{align*}F = ILB \sin \theta\end{align*}.

The direction of the force is found using the right-hand rule: The force is perpendicular to the plane formed by the current-carrying wire and the magnetic field direction.

2. The force experienced by a charged particle moving through a magnetic field is given by the equation \begin{align*}F = q \nu B \sin \theta\end{align*}.

The direction of the force is found using the right-hand rule but must be reversed if the particle is negatively charged. The force is perpendicular to the plane formed by the velocity vector of the charge and the magnetic field direction.

3. A charge traveling in a uniform magnetic field moves in a circle of radius

\begin{align*}r = \frac{m \nu}{qB}\end{align*}

4. The torque a current-carrying loop experiences in a uniform magnetic field is given by the equation

\begin{align*}\tau = IAB \sin \theta\end{align*}

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Jun 27, 2013