Shawn Payne, age 12, of Eugene, Ore., for his question:

WHAT ARE AM AND F M RADIO?

AM in radio stands for amplitude modulation, a broadcasting method in which the strength of the

carrier waves is changed to match changes in the audio frequency waves. Audio frequency waves are electric waves that represent the sounds of a radio broadcast.

FM stands for frequency modulation, a broadcasting method in which the frequency of the carrier waves is changed to match changes in the audio frequency waves. Frequency is the number of times an electric wave vibrates each second.

A broadcasting antenna sends out two kinds of AM radio waves: ground waves and sky waves. An FM radio antenna sends out waves that travel in the same directions as AM waves, but FM waves that go skyward are not reflected. Instead they pass through the atmosphere and go into space. Horizontal FM waves travel in what is called line of sight.