Extremely low frequency: Difference between revisions

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			[[File:Elfpics.jpg\|thumb\|ELF Devices]]
	Extremely low frequency (ELF) is the ITU designation for electromagnetic radiation (radio waves) with frequencies from 3 to 30 Hz, and corresponding wavelengths from 100,000 to 10,000 kilometers.ELF waves can also penetrate significant distances into earth or rock, and "through-the-earth" underground mine communication systems use frequencies of 300 to 3000 Hz. The frequency of alternating current flowing in electric power grids, 50 or 60 Hz, also falls within the ELF band, making power grids an unintentional source of ELF radiation.		Extremely low frequency (ELF) is the ITU designation for electromagnetic radiation (radio waves) with frequencies from 3 to 30 Hz, and corresponding wavelengths from 100,000 to 10,000 kilometers.ELF waves can also penetrate significant distances into earth or rock, and "through-the-earth" underground mine communication systems use frequencies of 300 to 3000 Hz. The frequency of alternating current flowing in electric power grids, 50 or 60 Hz, also falls within the ELF band, making power grids an unintentional source of ELF radiation.