Magnetic Tapes

You've probably magnetized lots of stuff before those paper clips. Ever tape record someone talking, or record a TV program on your VCR?

Magnetic tapes, like the ones you put in your tape player and your VCR, write the music by magnetizing small parts of the tape. The disk drives and floppy drives in your computer also magnetize small dots to store your files. Don't bring your magnet near your tapes or floppies! It can erase them.

Don't even think about erasing anybody else's floppies. It's a mean idea, and only pinheads would do it.

As you crumple a piece of paper, little areas bend and crackle. In the same way, as you magnetize a magnet, little areas of the magnet become magnetized. As these areas jump from one magnetization to another, they make crackling noise!

If areas jump from one magnetization to another, then the tape recorder can't record perfectly: it can only get within one jump of the right value. (It's like drawing with a pencil on the sidewalk: you try to draw a straight line, but it comes out bumpy when you hit all the little pebbles and grains in the cement.)

Experiment: Hiss on Audio Tapes.

If you have a boom box and a blank tape, you can hear the problem caused by the jumps in the magnetization. Put the blank tape into the tape deck, and slowly turn up the volume until you hear a hiss. You can tell the hiss is on the tape if it gets louder and softer as you push the volume up and down.

Be careful to turn down the volume again when you're done! The next person could ruin both the speakers and her ears. The next person could be you!