| C | H | A | P | T | E | R 21 |
| Magnetic Forces and Magnetic Fields |

This beautiful display of light in the sky is known as the northern lights (aurora borealis). It occurs when electrons, streaming from the sun, become trapped by the earth’s magnetic field. The electrons collide with molecules in the upper atmosphere, and the result is the production of light. Magnetic forces and magnetic fields are the subjects of this chapter. (Steven Nourse/Stone/Getty Images)

Copyright © 2007 John Wiley & Sons, Inc. All rights reserved.