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    Re: Test your magnetic compass.
    From: Alexandre Eremenko
    Date: 2012 Nov 16, 18:20 -0500

    I don't really understand, why alternating current produces a
    constant magnetic field.
    Ken confirms this but does not explain.
    But this is a phenomenon which I noticed long ago and can even measure
    with my compass. It is about 10 degrees, close to a wall electric switch.
    There are also constant magnetic fields produced by nails in the studs
    of an American house. (And by iron rods inside the concrete of Soviet
    And there is even a simple magnetic devise based on this,
    it is called the stud finder.
    But the field produced by AC wiring is stronger.
    On Fri, 16 Nov 2012, Ken Muldrew wrote:
    > On 2012-11-16, at 2:55 PM, Bill Morris wrote:
    >> Can some physicist or power engineer explain how an alternating current can 
    produce a constant magnetic field? Could corona discharge really account for 
    the observation or must we postulate rusty joints in transmission towers 
    acting as rectifiers?
    > AC power lines produce AC magnetic fields, but you have to be within about a 
    meter of the line for the strength of the B field to equal that of the earth. 
    DC power lines are becoming more popular due to advances in power 
    engineering. Currently there are only about one or two hundred DC high 
    voltage lines worldwide but this number will increase soon (at least power 
    companies seem to be marketing the safety of DC lines pretty aggressively, 
    and they do make sense for technologies such as wind power).
    > Ken Muldrew.
    > : http://fer3.com/arc/m2.aspx?i=121152

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