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Magnetic field of the Earth

  1. May 24, 2015 #1
    As we all know The Earth has a magnetic field. Why the objects on the surface of the Earth do not get magnetized? It is possible to measure the magnetic field frequency of the Earth?
  2. jcsd
  3. May 24, 2015 #2


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    They do. The magnetic field of earth is not strong enough to make powerful magnets, but it is sufficient to leave a measurable trace in some types of rock.
    It is a static field. It changes over long timescales, but not in a periodic way so "frequency" is not a very meaningful concept.
  4. May 28, 2015 #3


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    They do.

    Steel ships built in the Northern Hemisphere are magnetised in the opposite direction to those built in the Southern Hemisphere. The “magnetic detector” mines used in WW2 detected Northern built ships but not the Southern ones. Degaussing ships became very important. By cancelling or reversing the field “the ship could be made invisible”, but only to German magnetic mines.

    This appears to be the origin of the “Mare's Nest” now called the Philadelphia Experiment.
  5. May 28, 2015 #4


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    did you really mean frequency or field strength ?
    The Earth's magnetic field strength is measures by a number of sites around the world on a continuous basis
    These warn of the start of geomagnetic storms that produce aurora ... the upsets in the magnetic field is caused by changes in the interplanetary magnetic field produced by the Sun

    Magnetometers are used to detect fluctuations in the geomagnetic field. during the onset of a geomagnetic storm I have seen variations in the field of up to 40 - 50 nT ( nano Teslas). But even variations in the 15 - 30 nT range are quite significant

    To just quickly expand on mfb's comment and link on magnetised rocks.
    The discovery of magnetic striping of rocks on the seafloor was the final significant proof of seafloor spreading and the plate tectonics ( continental drift) theory

  6. May 28, 2015 #5

    Vanadium 50

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    I guess you could use the frequency of reversals, which is irregular, but of order 100 fHz.
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