# Tag Info

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The lift generated by magnetic field B on a superconductor of area S is: $$F = \frac{B^2S}{2\mu_0}$$ disregarding lateral forces and assuming superconducting cylinder (or similar shape) with area S at the top and bottom and height h, we need three forces to remain in the equilibrium: magnetic pressure on top, bottom and gravity ...

5

Yes, the Earth's magnetic field does rotate with the Earth. There is a simple way and a complicated way to explain this. Firstly the simple way: the magnetic north pole and the North Pole are not at the same point. That means if the magnetic field did not rotate with the Earth the magnetic north pole would rotate once around the North pole every 24 hours. ...

4

Circulating neutral particles will not by themselves create a magnetic field. However, if the neutral particles are moving through an existing magnetic field, and the neutral medium is conducting, then the magnetic field will induce a current via the Lorentz force. That induced current will in turn create it's own magnetic field, which may enhance the ...

4

Yes, the geomagnetic field does rotate with the earth. This is the reason why maps of the geomagnetic field overlaying geographic coordinates are reasonably accurate for a decade or two - and why a compass is still useful for navigation. (i.e. You do not need to know the time of day in order to correct for the magnetic declination cited on your map!) The ...

3

You can't generate power from a static magnetic field alone. In this context, the earth is just a permanent magnet, and a rather weak one at that. To generate electric power from that, you have to move electric conductors, like wires, thru the field in the right direction and with the right orientation of the conductor. If any electric power is taken from ...

3

Multiple sheets of steel work nicely to attenuate magnetic fields with higher frequencies but they are not great if you want to shield against small and constant fields. To shield the earth's magnetic field the best material has a high permeability with almost zero hysteresis. There are some metallic glasses, such as Ultraperm, Vitrovac or Metglas that I ...

3

Magnetic surveys are used for prospecting for oil or minerals. On top of the earth's magnetic field there are small contributions form magnetic materials in the surface rocks, especially granites. You can use this to either find large bodies of volcanic rock that migth have minerals or diamonds - or alternatively you can find large volumes with no magnetic ...

2

The north-seeking pole always points toward magnetic north, assuming it is only feeling Earth's magnetic field. A magnet has no idea (so to speak) which direction is geographic north. Any source that tells you that a magnet points geographically north is only as correct as the statement that geographic north and magnetic north are the same direction.

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The physical explanation for the origin of the geomagnetic field is that it is caused primarily by electric currents (moving charge) in the Earth's liquid outer core. The composition of the outer core is thought to be largely iron. The temperature in the core is above the Curie temperature of iron, which means the magnetic field of the core is not caused by ...

2

You don't need a separated electric charge for the Earth's core to generate a magnetic field, and you don't even need a ferromagnet. This experiment simulates the magnetic field generation by using a model of the core containing liquid sodium. Actually I'm not sure if they've got it to work yet, so maybe I should say may simulate rather than simulates. You ...

2

Apologies for the hasty questioning. I found the reference in the File Description of the wikipedia image description page. The model is apparently called the GUFM model, for which a good reference is Four centuries of geomagnetic secular variation from historical records. A Jackson, A R T Jonkers and M R Walker. Phil. Trans. R. Soc. Lond. A 358 no. 1768 ...

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Here is the home page for the GUFM model website. It also includes a link to a freely available pdf of the modern reference. Also of interest is the NOAA WEBSITE. GUFM MODEL HOMEPAGE NOAA PAGE Note that this model is based upon catalogs of geomagnetic field measurements, these did exist prior to 1800 - although as you would expect their quality and ...

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The stone contains a ferromagnetic material, which is a material with a spontaneous magnetization. In thermal equilibrium, such a material aligns itself to be magnetized in the same direction. But over a very large distance, you can reduce the bulk energy by randomizing the field direction, so that it pays to put in very large domain walls separating ...

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I don't know the name, but you can certainly do it. Just make a loop of wire and rotate it around a vertical axis. Use some brushes to allow the rotating loop to make electrical contact with your fixed circuit and take out the energy or spin the circuit with the loop. You will need some source of mechanical energy to spin the loop-that is where the ...

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Because the magnetic field does not align with the geographic axis, most places will show a variation between true north and magnetic north. However since some areas have an east variation and some areas have a west variation, there must be a border between those areas where the variation just happens to be zero.

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Also if a compass aligns in the direction of horizontal component of MF at that place does this mean that at any place horizontal component is directed towards the magnetic north ?? That's exactly what it means. That's the definition of magnetic north. If u look at a bar magnet's field lines not every tangent to the curve will pass through the north pole. ...

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Simply: if the line from your position to the magnetic North also goes through the geographic North, your magnetic declination will be zero. This happens at every point along the great circle that includes magnetic North and the North Pole. Note that in reality there are sufficient iron ore deposits in the earth to disturb the "ideal" picture above - see ...

1

What is the origin of the geomagnetic field? The Earth's magnetic field can't be a permanent bar magnet. Permanent bar magnets aren't that permanent. A bar magnet would only last a few tens of thousands of years before it decayed. That's extremely short in geological terms. The Earth's magnetic field has been around for billions of years. Something has to ...

1

This particular orientation sensing protocol is not wonted to me, but the following, given the data you cite, will indeed give you your orientation in space: Magnetometer gives $\vec{N}_0$ north direction (in general, not parallel to the "ground" because it has magnetic dip included); Gravity accelerometer gives $\vec{D}$ "down" direction; Then ...

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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. ...

1

The Earth rotates around an axis. Denote the unit vector directed along this axis (with the direction determined by the right hand rule) as $\hat z$. This rotational axis is key in finding "north". I'll assume a nice simple geometrically shaped Earth, either a sphere or an ellipsoid, and I'll assume a person who is not standing on the north or south pole. ...

1

You might be able to figure this out by looking at the following picture (source: http://www.unc.edu/depts/oceanweb/turtles/geomag.gif): As you can see, the field lines point into the earth.

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