4 ms·
Ah, but it does propagate. A time varying magnetic field generates an electric field. Though as you said, the motor does not make an efficient antenna.
by madengr 9y ago
Ah, but it does propagate. A time varying magnetic field generates an electric field. Though as you said, the motor does not make an efficient antenna.
- gji 9y agoThe electric field gets quickly attenuated in saltwater though, especially at high frequency: https://en.wikipedia.org/wiki/Communication_with_submarines https://en.wikipedia.org/wiki/Communication_with_submarines
- madengr 9y agoYep, but that E field is generated from currents in the lossy seawater, and those currents are induced by the magnetic field. If the seawater were a perfect conductor, the magnetic field would not propagate either. Free space impedance is 377 Ohms/meter; the ratio of E/H fields. Seawater is much, much lower, but the ratio is still there. If there's a propagating H field, there is a corresponding E field; that's the law according to Maxwell. The VLF antennas on the subs are trailing wires; electrically short dipoles. Those are mostly sensitive to E fields.