Question How does Earth have a magnetic field when it doesn't meet the electromagnetic requirements (an iron core is insufficient)?

[Space Crumpet]

A core tenet of electrical engineering is that to generate a current, you need three things: a conductor, a magnetic field, and motion. We assume the components are arranged appropriately, but then, quite simply, if you move a conductor through a magnetic field, you get current.

Alternatively, if you have a conductor, a current, and motion, you can generate a magnetic field. This is how an electromagnet works. However, the Earth has only a conductor (its core) and motion (its rotation) but no current, so how does it generate a magnetic field?

If I were in outer space with a molten sphere of iron, and then I tossed it up with a spin, it would not create a magnetic field. So how come we have one around the Earth?

 

[COLGeek]

See here: https://en.wikipedia.org/wiki/Earth's_magnetic_field

Hint...magma movement.

Here is a recent "Science Friday" segment that explained from a Martian perspective:

What Martian Geology Can Teach Us About Earth

The geology of Mars could provide a snapshot of what our planet was like as the crust was forming and plate tectonics began.

www.sciencefriday.com

 

[Space Crumpet]

I accept the motion of the core and, without loss of generality, its convection currents. It could be a hot swirling mess, but that still only gives us a conductor and motion; it does not provide the electric current that is also required to generate a magnetic field.

The Wikipedia article states the following: “The magnetic field is generated by electric currents due to the motion of convection currents of a mixture of molten iron and nickel.”

Unfortunately, this is circular reasoning because it presumes you get the electric current from the motion provided by the convection currents of the conductor (the molten core). However, for the motion of the conductors to generate current, you have to already have an electric field. Consequently, the Wikipedia statement is tantamount to saying, “If you already have an electric field (and conductors and motion), then you get a current that will then generate an electric field.

The fault could lie with the writers. There are not many good technical writers. Nevertheless, as it stands, my question is still unanswered.

 

[Catastrophe]

I found this rather good, no?

Earth's magnetic field - Wikipedia

en.wikipedia.org

Cat

 

[Space Crumpet]

Same Wikipedia article

 

[Classical Motion]

Iron can align and maintain it's magnetic directional(dipole) property from an outside source. While in the solid state phase. Probably much more in it's liquid phase. This can act like a M flux magnifier, if excited with an external field. A moving alignment. It twirls but stays aligned.

Our crust and probably our mantle in saturated with water. Water dissolves. Producing a constant inventory of ions. These ions do not have to flow. The earth's rotation is their flow. The relevant flow will be greatest in the equatorial plane. If one of those ion concentrations become aligned, more than the other concentration, there will be a net charge in rotation with the earth. Current. This current will produce a M field, which could align the center mush. And core magnify that M field. A self aligning core.

The very center of the earth might have less gravity than the area around it, letting the center be easily influenced.

 

[arturo.v.dominguez@gmail.]

A core tenet of electrical engineering is that to generate a current, you need three things: a conductor, a magnetic field, and motion. We assume the components are arranged appropriately, but then, quite simply, if you move a conductor through a magnetic field, you get current.

Alternatively, if you have a conductor, a current, and motion, you can generate a magnetic field. This is how an electromagnet works. However, the Earth has only a conductor (its core) and motion (its rotation) but no current, so how does it generate a magnetic field?

If I were in outer space with a molten sphere of iron, and then I tossed it up with a spin, it would not create a magnetic field. So how come we have one around the Earth?

However, the Earth has only a conductor (its core) and motion (its rotation) but no current, so how does it generate a magnetic field?

Well, I wouldn't go that far... there is such a thing as static electricity. Which with nothing but opportunity generates a current. Maybe we're looking for too a deep explanation on why the magnetic field exist.

Perhaps it's as simple as examining conductivity in combination to the path of least resistance and when those two cease to exist.

 

[billslugg]

The Earth's magnetic field is generated by the dynamo effect. The current in a conductor generates a magnetic field that generates current when the same conductor crosses it . And, yes, it appears to be circular logic. Once going it never stops, but how does it start? It must be "kick started". There must be a tiny magnetic field to start. This may come from any source. For example, in the starting up of a brand new automobile alternator, absent a battery to provide the needed field, it is sometimes required that one hit the shell with a hammer in order to jostle the atoms so they settle back into place influenced by the Earth's magnetic field and thus make a tiny current that cascades to the final amperage. The alternator will then run properly absent a battery. Remnant fields will persist in the iron core for the rest of the life of the alternator and the hammer will never be needed again.

The Earth's dynamo is powered by three sources of heat, remnant heat from the formation of the Earth, radioactive decay and the heat of crystallization of the iron core. This causes liquid iron at the core surface to rise, in Earth's case, at the equatorial belt. It travels towards the poles and subducts back for another cycle. The Coriolis force due to Earth's rotation causes the flow to bend westward. By the left hand rule for electrons, which have higher mobility than the positively charged atoms in the melt, the electron flow westward under the equator causes the South Pole area of the Earth to assume a north magnetic pole. On Earth the north geographic pole is the south pole of a magnet. A magnetic north pole being defined as that pole of a compass needle which points to the north.

 

[Gibsense]

The Earth's magnetic field is generated by the dynamo effect. The current generates a magnetic field that generates current when a conductor crosses it. And, yes, it appears to be circular logic. Once going it never stops, but how does it start? It must be "kick started". There must be a tiny magnetic field to start. This may come from any source. In the starting up of a brand new automobile alternator, absent a battery to provide the needed field, it is sometimes required that one hit the shell with a hammer in order to jostle the atoms so they settle back into place influenced by the Earth's magnetic field and thus make a tiny current that them cascades into the final amperage. The alternator will then run properly absent a battery. Remnant fields will then persist in the iron core for the rest of the life of the alternator and the hammer will never be needed again.

The Earth's dynamo is powered by three sources of heat, remnant heat from the formation of the Earth, radioactive decay and the heat of crystallization of the iron core. This causes liquid iron at the core surface to rise, in Earth's case, at the equatorial belt. It travels towards the poles and subducts back for another cycle. The Coriolis force due to Earth's rotation causes the flow to bend westward. By the left hand rule for electrons, which have higher mobility than the positively charged atoms in the melt, the electron flow westward under the equator causes the South Pole area of the Earth to assume a north magnetic pole. On Earth the north geographic pole is the south pole of a magnet. Thus the north pole of a compass needle points north. A magnetic north pole being defined as that pole of a compass needle which points to the north.

Wow!

 

[George²]

However, the Earth has only a conductor (its core) and motion (its rotation) but no current, so how does it generate a magnetic field?

Well, I wouldn't go that far... there is such a thing as static electricity. Which with nothing but opportunity generates a current. Maybe we're looking for too a deep explanation on why the magnetic field exist.

Perhaps it's as simple as examining conductivity in combination to the path of least resistance and when those two cease to exist.

I don't know why you are misled by the name. For the generation of an electromagnetic field, it is not necessary to have an electromagnet and an electric current.

 

[billslugg]

It is true that there are permanent magnets that don't need an electrical current. However, there is an absolute dictum in physics. A magnetic field can only be produced by a moving charge. This is what got Einstein to formulate Special Relativity. He could not understand why the magnetic field was observer dependent. An electron riding down the street does not measure a magnetic field due to it. An observer on a park bench will measure a magnetic field as the electron passes by. The explanation is that the moving electron is Lorentz contracted relative to the observer, thus exerts a force on the observer.
But how do permanent magnets work? The charged electrons are moving about in their shells. This is the motion which is needed.

 

[arturo.v.dominguez@gmail.]

I don't know why you are misled by the name. For the generation of an electromagnetic field, it is not necessary to have an electromagnet and an electric current.

I do not agree that I am being misled nor that I misunderstand the question:

A core tenet of electrical engineering is that to generate a current, you need three things: a conductor, a magnetic field, and motion.
The above statement comes directly from Space Crumpet's original comment #1.

Then he asks?

If I were in outer space with a molten sphere of iron, and then I tossed it up with a spin, it would not create a magnetic field. So how come we have one around the Earth?

At which point I offer that static electricity is a current that exist but will only shows activity once a conductor of some kind presents itself.

 

[billslugg]

You are correct: A current will occur when one area of static charge moves through a conductor to neutralize another area, that one of opposite charge. A current can also be generated by chemical action and sent through a conductor. A current is generated any time any conductor moves across a magnetic field line. All currents produce magnetic fields. All magnetic fields have moving charges associated with them.

 

[Classical Motion]

Let's put a charge on a 45 RPM record and play it at 78 RPM. Did we get an M dipole in the center? Does that dictum hold true? It should. If it doesn't, increase charge and increase speed. A compass suspended over the record should deflect.

If we put a high mu liquid in the center, will the dipole flux(B) grow in strength? A metal core. When we put iron in an air core solenoid and keep the same charge motion(current), B increases.

I should have kept my turn table.

 

[arturo.v.dominguez@gmail.]

Man, thanks for letting me know. I guess I shouldn't be playing my 45's at 78 RPM's, on my turntable, if I want to keep them working as they should ...regardless of how far out they make me feel.

 

[Classical Motion]

Put a few drops of ferrofluid in the center. Look closely and see if it has a tendency to stand up.

 

[Classical Motion]

You can discharge the charge on the record and it should play just fine. I would try to play it while it is charged, just to see what happens.

 

[Classical Motion]

You may charge a record by rubbing record on a cat.

 

[billslugg]

A charged particle sitting on the edge of a record would indeed cause a dipole field similar to Earth's. Earth's field can be approximated by a flow of electrons on the Equator traveling east to west.

 

[Classical Motion]

Let's replace the vinyl with Al foil. And charge it. This "free charge" charge field should be uniform because of repulsion. Do we get the same M field when rotated?......or because the charge is free and not sticky, will the free charge line up to react and counter the generated M field from rotation?

 

[billslugg]

Looking down on a charged metal disc that rotates about the central axis clockwise will generate a magnetic field similar to Earth's, with south on top and north on bottom as viewed from outside. On the disc, a given charge will not see the charge around it moving, but it will see the charges at 180° on the disc as moving to the right. To the observer on the disc, those moving electrons will generate a magnetic field which will be seen as pointing upward. This wil cancel some of the original magnetic field. I guess everything will just cancel out.

 

[Classical Motion]

Looking down on Earth, the Earth rotates CCW. The polarity of the M field starring you in the face depends on the polarity of the net charge. It could be north or south.

It happens to be south. That means net negative charge. IS powering the M field....or net measuring part of it.This can easily be verified with a few current loops and a compass.

The field we measure and call Earth's M field might not be a singular field, but might be the result of counter induction.

Like transformer action. The little we measure might be just the little left over that does not get cancelled.

That would be pretty wild. And if it is a balance of counter poles.....it could be an easy dynamic to switch poles. Because both poles are always there.

Nyuk nyuk.

 

[billslugg]

A net negative charge on the equator traveling eastward will generate a magnetic field pointing to the north geographic pole. This is opposite to reality. Our planet's north geographic pole is the south pole of a magnet. The north pole of a magnet being defined as that pole which points to the geographic north on Earth when suspended by a thread.

 

[Classical Motion]

It doesn't matter which starting pole is agreed upon. Just like it doesn't matter if you use positive current or negative current. Just change the net charge polarity to your liking. Counter induction, transformer action, was the point.

It's all academic supposition for we can't go there and verify anything. But that steep declination implies it's deep. And not that long if a bar. Small, short dipole at fountains. Just my guess.

The field we measure might be the counter field. An outer rarefied dipole.

That's pure spit ball. Only because it might be possible.

 

[billslugg]

There are conventions in Electrical Engineering that we use to make sure the motors turn in the correct direction. They are the left hand rule for electrons and the right hand rule for positive charges.
There is also a general rule that any motion of a magnetic field through a conductor results in a current that opposes the initial force. In this case it makes no difference which charges are moving or which direction the field is moving. Counter electromotive force can crush beer cans. I've done it with a capacitor bank and a coil I made. I had 10,000 microfarads charged to 450 volts, about the same amount of energy as a 22 shell. I made a coil of probably 5 turns of #2 copper wire, put a can in there, discharged it. Turned the can into an hourglass. Neighbor came over wanting to know who got shot.