Re: How the current produce for our earths magnetic field ?

Question: How the current produce for our earths magnetic field?

Hello Varadha,
You asked a very interesting question!  The earth’s magnetic field is 
produced by a complex “mix” of physical phenomena.  In the simplest 
sense, the earth acts like a giant motor/generator because moving, 
electrically charged conductive materials create the magnetic field 
similar to the way a generator does.  (When electric current flows 
through the wires in a generator a magnetic field is produced that 
surrounds the wire).

The actual mechanism within the earth is of course, a lot more 
complicated, but works on the same principles.  The inside layers of the 
earth are responsible for producing and sustaining the magnetic field.  
The earth’s outer core is composed mainly of liquid iron.  The flow of 
this liquid core moves through a magnetic field, and like a generator, 
produces an electric current through the iron.  Now, the electric current 
within the flowing metal produces a stronger magnetic field.  OK, now 
this is starting to sound like a contradiction, or similar to “What came 
first- the chicken or the egg?”  What came first the “magnetic field” or 
the “current”?

But, in fact, that is how the earth’s magnetic system works.  The earth 
needed a starting, or “seed” magnetic field to produce the electric 
current within the molten iron in the outer core.  This seed magnetic 
field came from the sun.  So, the sun’s field produced an electric 
current in the moving iron.  The physically moving liquid iron (with 
flowing electric current) generates what we call the earth’s magnetic 
field.

But a generator that loses its source of power would stop producing 
electricity and magnetic fields.  In the same way, the earth needs a 
source of energy to sustain the flow of the molten iron, and the 
resulting magnetic field.  This energy comes from the following:
The central core of the earth is mostly solid iron at a temperature of 
around 4800°C.  The reason the metal is solid at that incredibly high 
temperature is because of the enormous pressure at that depth.  When the 
liquid iron from the outer core comes to the boundary of the inner core, 
some of the iron “freezes” into solid, and joins the inner core.  The act 
of freezing, or solidifying releases energy into the surrounding fluid.  
This energy raises the temperature, and lowers the density of this 
surrounding fluid.  This lower density iron tends to rise and thus gives 
the driving force for the currents of molten iron.

If the earth were not rotating, the rising currents of molten iron would 
not produce the nice north-south magnetic field that surrounds the earth, 
but would produce random, mixed up magnetic fields.  But, because the 
earth IS rotating, the molten iron is forced to flow in organized eddy 
currents which focus the magnetic field into what we observe on the earth.
The links below go into more detail on the cause of these eddy currents 
and also give more details on the information that I have written.

I hope that this is helpful to you.
Best Regards,

Jay Shapiro
Mad Scientist


 http://www.pbs.org/wgbh/nova/magnetic/reve-drives.html http://www.geomag.nrcan.gc.ca/mag_fld/fld-eng.php