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What is the reason for the Earth to behave like a bar magnet and have poles (North and South poles)?

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    $\begingroup$ Have you read Wikipedia's take on this? $\endgroup$ – ACuriousMind Nov 3 '14 at 19:26
  • $\begingroup$ Ya but I am not satified with only that $\endgroup$ – Sushant23 Nov 3 '14 at 19:27
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    $\begingroup$ @Sushant23 The exact reason for Earth's magnetic field is still an active field of research. sciencenews.org/article/spinning-core astro.berkeley.edu/~gmarcy/astro160/papers/… $\endgroup$ – DavePhD Nov 3 '14 at 20:24
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    $\begingroup$ two seperate articles, just looks like one link but really two links $\endgroup$ – DavePhD Nov 3 '14 at 20:36
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    $\begingroup$ I think the question would be improved (and attract some up votes) if you elaborated on what in the Wiki article was inadequate -it would be easier to tailor the answer to the question as well. $\endgroup$ – paisanco Nov 3 '14 at 23:03
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The Earth's magnetic field is caused by eddy currents in the liquid parts of the planet's interior. We believe the field is not due to a permanent magnet because: (1) Its direction and strength change over time, and (2) the planet's interior is hotter than the Curie temperature of its elements, and so a permanent magnet would not retain its magnetism. However, saying the field is due to eddy currents is not sufficient. Simply swirling around a conductive fluid does not produce a magnetic field. There has to be some source of electric current to make the whole process work, and we don't know what that source is. Several possibilities have been proposed. Examples include: (1) Gravitationally separated elements produce a voltage difference, as in a battery; (2) Gravitationally separated elements combined with the temperature differential between the Earth's core and its mantle creates a thermocouple junction that produces voltage, and therefore current; and (3) Flowing electrons produced by Beta decay of radioactive material in the core. However, none of these explanations are accepted as proven, and some are thought to be highly unlikely. So the source of the electric current remains a mystery.

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    $\begingroup$ Actually, there is a near consensus that the source of current is the magnetic field itself which generates it in the moving fluid through the Lorentz force, resulting in a self-exciting geodynamo. The three ideas above are not considered adequate, both because they are too weak and because they cannot explain geomagnetic reversals. See Roberts and Glaztmeier, "Geodynamo theory and simulations", Reviews of Modern Physics, vol. 72, page 1081 (2000). $\endgroup$ – A. Newell Aug 13 '17 at 17:17
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When we say that the Earth's field behaves "like a bar magnet", we have in mind a field that is approximately dipolar. So while it is true that a geodynamo powers the field (see this Wikipedia page), we need to say a little more. First, the rotation of the Earth organizes the flow, tending to align it with the rotation axis. Second, the magnetic field from a finite source looks increasingly like a dipole as we get further away from it; in a multipole expansion, the higher the order of the term, the faster it drops off. The surface of the Earth is at a radius that is roughly twice the radius at the core-mantle boundary, enough distance for a substantial reduction in non-dipole contributions (see Merrill and McElhinny, "The Magnetic Field of the Earth: Paleomagnetism, the Core, and the Deep Mantle", Academic Press 1998, chapter 2). Finally, the magnetic field in the core could have a large toroidal component, but we know little about its strength because toroidal components don't pass the core-mantle boundary (Merrill & McElhinny chapter 9.2).

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Earth behaves like a magnet because the molten iron core of the earth interacts with the movement of electron on the surface of the planet. Use a compass to determine the direction of the north and south magnetic poles.

So, the earth behaves magnet

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    $\begingroup$ Be aware this is an old question. Your answer does not add anything new to David's accepted answer and it is also quite unclear. $\endgroup$ – Jonas Greitemann May 25 '15 at 10:21

protected by Qmechanic May 25 '15 at 9:33

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