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Radio waves are a part of the electromagnetic spectrum. We identify the various parts of that spectrum by wavelength. The wavelengths of radio waves can vary from about one millimeter to about 100 kilometers, so they cover quite a wide range. Consequently radio waves are grouped into subcategories by their use. The shortest are microwaves, followed by TV and FM radio, shortwave radio, AM radio, and the frequencies used by ships and aircraft, which are the longest wavelengths.
Astronomers have discovered that the universe is full of radio waves, which are emitted by stars, quasars, interstellar dust, and other bodies. Radioastronomers have made some fascinating discoveries about the universe and its origins by studying these waves.
I am supposing it could get longer than this, but the normal range which most humans hear sound is in the range of 20 Hertz (Hz) to about 20, 000 Hertz (Hz), or 20 kilohertz. Given a speed of sound at around 343 meters per second, that would give us a wavelength of 17 meters to .017 meters, or 17 millimeters. Compare a meter stick (17 of those, laid end to end) to 17 of the tiny little black marks on the meter stick. Also, keep in mind this is within the normal hearing range of humans. Dogs, for example, can hear much higher pitched frequencies than humans do. Bats use sound frequencies to help them navigate as they fly, using frequecies much higher than this. Elephants are known to communicate with low-frequency rumbles, too low to be detected by human hearing, which can be heard by other elephants miles away.
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