Projects For Learning: Static Sound

Materials Needed:

• radio with antenna
• balloon, 9in. (23 cm)
• piece of wool cloth

Procedure:

Note: Do this on a day with low humidity for best results.

• Turn the radio to a very low volume.

• Inflate the balloon and tie it.

• Quickly rub the ballon against a piece of wool 10 times or rub the balloon against your clean, dry, oil-free hair.

• Listen as you hold the balloon near, but not touching, the radio antenna.

Results:

A single pop is heard from the radio as the balloon nears the antenna.

Why?

The crackling sound of static during a thunderstorm is caused by radio waves, but not waves sent out from the radio station. The static sound is from radio waves sent out by lightning. Just as the built-up electrical charge on the balloon produced radio waves that were transmitted through the radio as a single popping sound, the electrical charges in lightning produce radio waves that are transmitted through the radio as sounds we know as static. Radio waves are produced by electrical charges, and a flash of lightning produces 10,000 times the electric current nedded for for an electric iron.