Steven Wight, age 7, of Salt Lake City, Utah, for his question:

HOW IS AN AUDIO TAPE RECORDING MADE?

Here's how an audio tape recording is made:

Tape passes from the supply reel to the take up reel over a soft rubber pinch roller, which presses the tape tightly against a motor driven metal rod called the capstan.

Before the tape reaches the capstan it touches the erase head, which erases any previous recording. Then the tape touches the recording head.

The recording head is an electromagnet. There is a small gap between the poles of the magnet. The electromagnet is magnetized by electric waves from a microphone. These waves have been strengthened by the recording amplifier. A magnetic field is created in the gap between the magnet's poles.

As the tape crosses the recording head, it touches the head at the gap. The changing magnetic field magnetizes particles on the tape in a pattern like that of the sound waves entering the microphone. As soon as the recording is completed, it can be played back.

The playback head picks up the tape's magnetic pattern, which creates electric waves in an electromagnet inside the head. The playback amplifier strengthens these waves enough to operate a loudspeaker, which changes them into sound.