can magnetic fields be made to spin?

[bwanaaa]

For example, the van allen radiation belt is a magnetic field, teardrop shaped away from the sun due to the solar wind. Does the earth's rotation cause the axis of that eardrop to be slightly off the sun's ray?

 

[sao123]

Originally posted by: bwanaaa
For example, the van allen radiation belt is a magnetic field, teardrop shaped away from the sun due to the solar wind. Does the earth's rotation cause the axis of that eardrop to be slightly off the sun's ray?

the van allen radiation belts are regions of intense radiation trapped by earths magentic fields. they are not the magnetic fields themselves.
the innerbelt is composed primarily of trapped protons, and the outer belt is composed of trapped electrons.

The reason for the teardrop effect is that solar wind from the sun, excites these particles enough that they escape the earths magentic field, however solar wind is not nearly as stong in the earths shadow cone, therefore producing the teardrop effect.

The current theory about how a planet produces a magnetic field is called the Dynamo theory. Because the magnetic field poles, and the earths rotation poles are off by 11-12 degrees, it is unlikely that the magnetic field orbits as part of the earth, similar to how the atmosphere does.

 

[Biftheunderstudy]

I'm not sure if the Earths magnetic field is twisted at all, I doubt even the sun's gravity is enough. Twisting of magnetic fields does happen(at least theoretically)on the cosmological scale. Around neutron stars and black holes the field is thought to be very strong and very twisted. In large molecular clouds the magnetic field is slightly twisted, we can see this since the cloud is twisted along with the field lines making kind of a coil in the sky.

 

[silverpig]

They certainly can. That's how MRI works


As to your actual question it doesn't really have to be the magnetic field spinning to cause that. It's just the distortion of a field by an external influence. Try to put a bar magnet underneath a piece of paper and sprinkle some iron filings on it. You'll see the magnetic field lines in the pattern of the iron filings. Now bring a second magnet near to your paper and slightly shake the paper. You'll see the effect of the second magnet's field on the first.

 

[bwanaaa]

i probably need more words to resolve my question and permit and answer. With an MRI, what happens is the intense magnetic field aligns the spin of the protons. The decay to randomness is then measured. Since the magnetic resonance of different materials is identifiable, an image is thus constructed. Aligning the spin of a proton (or electrons) is NOT what I am asking about. Rather, the stupid experiment I am thinking about is this:
imagine a bar magnet standing on its south pole with the north pole at the top. The magnetic field will look like an apple (sort of). Now what happens when the bar magnet is rotated ALONG its axis. The north and south poles DO NOT GO ANYWHERE.. Does the magnetic field change in any measurable way? Maybe I am screwing up, but I cannot induce a current in a wire no matter where I put the wire. This tells me that although the magnet is in fact spinning, the magnetic field is not.

 

[Matthias99]

Originally posted by: bwanaaa
i probably need more words to resolve my question and permit and answer. With an MRI, what happens is the intense magnetic field aligns the spin of the protons. The decay to randomness is then measured. Since the magnetic resonance of different materials is identifiable, an image is thus constructed. Aligning the spin of a proton (or electrons) is NOT what I am asking about. Rather, the stupid experiment I am thinking about is this:
imagine a bar magnet standing on its south pole with the north pole at the top. The magnetic field will look like an apple (sort of). Now what happens when the bar magnet is rotated ALONG its axis. The north and south poles DO NOT GO ANYWHERE.. Does the magnetic field change in any measurable way? Maybe I am screwing up, but I cannot induce a current in a wire no matter where I put the wire. This tells me that although the magnet is in fact spinning, the magnetic field is not.

I would think that a wire that is parallel to both the 'ground' and the magnet would see some sort of changing magnetic field -- but maybe not. The field is definitely symmetrical around the vertical axis, so perhaps rotating it around that axis does not produce a... gradient thing in the field (whatever it's called... it's been a while).

But I am most definitely not a physicist, nor even an electrical engineer. I switched to CS because I wanted to have the computer do the math for me rather than the other way around.

 

[sao123]

Originally posted by: bwanaaa
i probably need more words to resolve my question and permit and answer. With an MRI, what happens is the intense magnetic field aligns the spin of the protons. The decay to randomness is then measured. Since the magnetic resonance of different materials is identifiable, an image is thus constructed. Aligning the spin of a proton (or electrons) is NOT what I am asking about. Rather, the stupid experiment I am thinking about is this:
imagine a bar magnet standing on its south pole with the north pole at the top. The magnetic field will look like an apple (sort of). Now what happens when the bar magnet is rotated ALONG its axis. The north and south poles DO NOT GO ANYWHERE.. Does the magnetic field change in any measurable way? Maybe I am screwing up, but I cannot induce a current in a wire no matter where I put the wire. This tells me that although the magnet is in fact spinning, the magnetic field is not.

you are correct.

 

[bwanaaa]

how then can a magnetic field be made to spin? If i cannot get it to spin by spinning the magnet then there must be another way to construct the same kind of magnetic field that is spinnable.

 

[Geniere]

Originally posted by: bwanaaa?With an MRI, what happens is the intense magnetic field aligns the spin of the protons. The decay to randomness is then measured. Since the magnetic resonance of different materials is identifiable, an image is thus constructed.

Only the first sentence above is correct. In addition to the strong magnetic field, a weaker field is applied to create a gradient of magnetic flux. The result is each pRoton has a slightly different tilt than its neighbor, thus a means to provide positional information. A radio signal is transmitted causing a very small shift in tilt. When the tilt alters a pHoton is emitted with a frequency characteristic to the degree of original tilt therefore unique to the location of the pRoton. The frequency of the emitted pHotons is used by software to generate an image. Only hydrogen is imaged, as heavier elements require much stronger magnets. Randomness of tilt only returns when the patient is removed from the device.

Originally posted by: bwanaaa? I cannot induce a current in a wire no matter where I put the wire. This tells me that although the magnet is in fact spinning, the magnetic field is not.

If the magnet has a cylindrical shape and is rotated along the long axis, the flux will everywhere remain constant. No current is generated in a wire unless it experiences a change in flux.

 

[silverpig]

A magnetic field basically is a spin. It's like asking if you can make a torque spin.

 

[bwanaaa]

thank you for your insightful replies. That the atoms responsible for a magnetic field move without a corresponding movement of the field is illuminating for me. The potential generated by one set of atoms is sustained as the new set move into position. Microfluctuations in the potential might be the only clue as the crystalline structure (or random array) of the atoms results in slightly varying locations of the atoms generating a particular field line. Alternatively, the motion may smooth out the bumpy microfluctions of the field lines generated by a static magnet. In any event we are talking about might small changes in field strength over relatively enormous distances

To go off on a tangent,How does a plasma then get spun up in a tokomak? I've got to go to wikipedia now...

 

[Roguestar]

Remember that field lines are simply drawn on diagrams to help our understanding. A magnetic field is actually a volume and a smooth transition from pole to pole. Regarding plasma, it flows in a donut-shaped volume surrounded by circular magnetic coils which induce a current within the plasma. This, combined with laser energisiation of the particles in the plasma causes it to heat up and move around the donut (toroidal) shape, creating a current flow of its own, if I recall A-level physics correctly...

 

[bwanaaa]

current can only be induced in a conductor by a MOVING magnet.

reading the wiki on tokomak and comparing it to a stellerator is instructive. but neither indicates what gets the plasma moving.

 

[Roguestar]

The conductor ie: the plasma is moving. It can be either one as long as the flux in one field cuts perpendicularly to the other.

 

[bwanaaa]

i guess the only way to accelerate the plasma is then to pulse the magnetic field

 

[patentman]

See this Link

See this link as well

I think magnetic fileds spin when solar flairs shoot up from sun's surface, when an effect like magnetic reconnection occurs.

 

[Roguestar]

How it was explained to me was not that the magnetic field itself spins, it only seems to spin if the ferro/para-magnetic material itself spins. Like if you consider the hypothetical field lines to be coming out of the spines of a cactus, and the trunk being the magnet itself, the spines do not move independently of the trunk.

If you know what I mean (probably a bad explanation of what I'm visualising here...).

 

[bwanaaa]

@roguestar
i initially thought as you do. but the understanding that a magnetic field is just lines of POTENTIAL made me realize that it doesn not really move when the magnet generating it spins on its axis. In other words, if there is a plasma whirling around a magnet, it will not change its behavior if the magnet spins or not. This is why I cannot generate a current in a wire, no matter where i position it around a spinning magnet.

@patentman
the concept of magnetic reconnection is a little vague to me. The release of energy stored in a magnetic field requires a 'plasma under duress' as i see it. i am not talking about mixing magnetic fields nor i am not talking about a plasma. i am simply thinking about a magnetic field. The whole idea of 'action at a distance' is hard to swallow sometimes because i dont dont know what it is that is conveying the force. Magnetic fields are not made of photons, particles or anything else we know of. There is no PARTICLE or WAVE there. The link in fact you pointed me to was a little misleading-it spoke about the earth's magnetic field and the solar wind as 'plasmas'. The solar wind I'll buy as a plasma, but the earth's field? But the whole idea of a boundary layer is interesting anyway. Makes me wonder about a new way to squeeze the plasma in a tokomak-get another field to compress the first. If a sort of leverage can be achieved then greater forces can be generated with smaller currents in the electromagnets.

 

[Roguestar]

But if you coil the wire a spinning magnetic field will induce a current in it...

I think you've lost me!

 

[patentman]

Originally posted by: bwanaaa
@patentman
the concept of magnetic reconnection is a little vague to me. The release of energy stored in a magnetic field requires a 'plasma under duress' as i see it. i am not talking about mixing magnetic fields nor i am not talking about a plasma. i am simply thinking about a magnetic field. The whole idea of 'action at a distance' is hard to swallow sometimes because i dont dont know what it is that is conveying the force. Magnetic fields are not made of photons, particles or anything else we know of. There is no PARTICLE or WAVE there. The link in fact you pointed me to was a little misleading-it spoke about the earth's magnetic field and the solar wind as 'plasmas'. The solar wind I'll buy as a plasma, but the earth's field? But the whole idea of a boundary layer is interesting anyway. Makes me wonder about a new way to squeeze the plasma in a tokomak-get another field to compress the first. If a sort of leverage can be achieved then greater forces can be generated with smaller currents in the electromagnets.

The concept of magentic reconnection is a little vague to everyone at this point. I'm not certain anyone really understands how it works, but its being looked into as a possible alternative energy source. The existance of magentic reconnection has primarily been shown during solar flares, where it is thought that it is the source of the much hotter areas (as in millions of degrees hotter) seen near the tip of some solar flares.

As for Earth's atmosphere comprising a plasma, I though this was relatively well known.

See, e.g.,:

http://science.nasa.gov/newhome/headlines/ast07sep99_1.htm

http://pwg.gsfc.nasa.gov/istp/news/9812/solarwind.html

 

[bwanaaa]

@roguestar
a spining field will induce a current. my point is that a spinning magnet does not cause a spinning field

@patentman
thank you for the links. yes the fine distinction is that the magnetosphere is the field and the plasmasphere is the actual collection of ions generated as a result of the solar wind slamming into our atmosphere. the effect of the plasmasphere on our magnetosphere could be deduced by comparing the magnetosphere of a relatively plasmaphere-less planet, like mars. my conjecture would be that the magnetosphere would not be deformed much at all there and resemble much more of an apple than ours, which is a teardrop with a tail 1000 earth radii long.

regarding a spinning magnetic field, i think i found a way to make one. imagine a long bar magnet whose cross section is a star. This thing would look like a long gear. If the magnet is stood on its south pole, the magnetic field will have maxima and minima corresponding to the sprockets and divets of the cog. Spinning this thing will generate spinning field lines.

 

[Biftheunderstudy]

My guess would be that in a bar magnet the B field is acting in the phi direction, therefore when you spin the magnet in the phi direction you are not changing the field, you are just changing the length of the vector which does not induce a current. When you translate the magnet you change the direction of the vector which does induce a current.

The problem with this model is that the B field is not entirely Phi direction, there is some thickness to the bar which would change direction very slightly, the reason you can't get a current induced from it is that the effect is rediculously tiny, proably nano or micro amps.

I'm pretty sure a spinning conductor creates a magnetic field, however it is a tiny effect. Look up London Moments which is the field created by a spinning superconductor.

P.S.
Incidentally, spinning superconductors also create a gravitomagnetic field:Q