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Author Topic: What flows in a magnetic field?  (Read 7485 times)

Offline Ben Rios

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What flows in a magnetic field?
« on: 21/05/2010 08:30:02 »
Ben Rios  asked the Naked Scientists:
   
Hi Chris,

I was wondering what flows in a Magnetic field?  Electrons flow to create electricity and photons surf along to create light.  What is in the giant field that protects the earth from the various rays that try to strip life off the planet?

I am a big fan and have been newbielink:http://www.thenakedscientists.com/HTML/podcasts/ [nonactive], but not all of them, there are are so many hours left to listen to.  If you already addressed this issue, could you please let me know.  

Thank you for any help you can,

Ben, from Brooklyn

What do you think?
« Last Edit: 21/05/2010 08:30:02 by _system »


 

Offline daveshorts

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What flows in a magnetic field?
« Reply #1 on: 21/05/2010 09:05:38 »
A field is really a mathematical construction, it is a way of representing what direction something will move for some reason. So as well as gravitational, electrical and magnetic fields you can construct a flow field in a fluid (where a particle put in the fluid will move), or something more obscure.

An electric field is distinct from electricity. An electric field is a representation of how a massless positively charged particle would move in a space, so it would move away from positive charges and towards negative ones.

Electric current is where the electrons are actually flowing in a wire, so there need to be free electrons to flow, you can get electric fields in a perfect electrical insulator, but not electric currents.

So nothing real has to flow for a field to exist.

A magnetic field is defined as how a massless North magnetic pole would move, so away from north poles and towards south. This is slightly complicated by the fact that free magnetic poles don't exist due to the nature of magnetism, they are always associated with a south pole.

So the answer to the question is that nothing in flowing in the field, it is just mathematically useful to think of something flowing.

The obvious next question is what is a magnetic field...
This is slightly more complex, it is a relativistic adjustment to an electrical field. Because in an electric current the positive and negative charges are moving at different speeds, relativity will affect the differently, and when you do lots of hard maths, something which looks like a magnetic field falls out as an adjustment to the electric field.

So the earth's magnetic field, is actually just part of the electric field of the electrons and protons in the metallic part of the earth's core. (the field is thought to come from convection currents in the molten convecting iron and nickel core of the earth.
« Last Edit: 21/05/2010 11:12:48 by daveshorts »
 

Offline djdave

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What flows in a magnetic field?
« Reply #2 on: 21/05/2010 11:06:28 »
The Magnetic Feild changes from time to time depending on the speed of the Earth and the Speed of the Earths Core.
 

Offline Ben Rios

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What flows in a magnetic field?
« Reply #3 on: 24/05/2010 18:05:13 »
Dave,
 Thank you for your response.  It is very cool to get an answer to the question which has been sticking with me for a long time.  Understanding the that a field is a mathematical representation of an area of potential, like the the electrical field which is separate from electricity, is very helpful.

My curiosity is further piqued by the fact that particles are attributed to transferring energy as in electricity with a motor, or what I understand a photon does to a solar sail.  It seems that something having to do with magnets can do things like protect the earth from cosmic rays, and such, or a bar magnet moving iron fillings into a pattern might transfer a similar force.  There are measurements for the "wear" that a magnet goes through when atracts or repulses, as if something is given up in the process.  Is the force already in the objects effected by a magnet and the relativistic adjustment to an electrical field is just activating the objects' own energy, or is the magnet exerting a force through something, i.e. photon, but not a photon, onto the objects?
 

Offline daveshorts

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What flows in a magnetic field?
« Reply #4 on: 25/05/2010 09:51:37 »
Quote
It seems that something having to do with magnets can do things like protect the earth from cosmic rays, and such, or a bar magnet moving iron fillings into a pattern might transfer a similar force.

The cosmic ray protection is because of the deep interconnection between electric and magnetic fields. A moving charged particle moving through a magnetic field will feel a force, and in quite a complex way this means that the particle will end up spiralling along the magnetic field line. So the particles approaching the earth tend to hit at the north and south poles.

All magnets are electromagnets, just in a bar magnet the electric currents are in the electrons orbiting the atoms. If you imagine two identical loops of wire, directly above one another with electric current moving through them in the same direction the electrons are moving in circles in the same direction.

 This means that the electrons are stationary to one another, and of course the nuclei are stationary to one another, so all the repulsive forces are the same, however the electrons are moving relative to the nuclei.The relativistic adjustment increases the force (like relativistic mass) so the electrons are attracted to the nuclei slightly more than the would be if stationary and the two loops attract.


 If the currents are going in opposite directions, the relative speed of the electrons is larger than the relative speed of the electrons an nuclei so the repulsive force is larger than the attractive one and the loops repel

The electrons are moving very slowly mm/s so the relativistic adjustment is trillionths of the charge of the particles, but the electric force is so immensely strong that this is still a very significant force.

A perfect magnet shouldn't be affected by applying a force to things, I think the wear that you refer to on ferromagnets (the one you pick up) is because steel and other ferromagnets are made up of trillions of atomic magnets which have been aligned to form a macro scale magnet. These atomic magnets never loose any magnetism, though they can become less aligned with time and abuse so the macro scale magnet can become weaker.

Particle physicists do talk about the electro-magnetic force (once you take into account relativity they are the same thing) being mediated (applied) by particles called virtual photons. These transfer the electro-magnetic force at the speed of light, but themselves have no energy, but at that point you essentially have a great big pile of equations and there are solutions to the equations, but what you call real is deeply philisophical.
 

Offline lunar11

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What flows in a magnetic field?
« Reply #5 on: 29/05/2010 10:00:04 »
Hi.
But, no one has mentioned 'virtual photons' which are responsible for field attraction and repulsion. Right?
Lunar
 

Offline acsinuk

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What flows in a magnetic field?
« Reply #6 on: 07/06/2010 10:01:01 »
Dave
"This is slightly more complex, it is a relativistic adjustment to an electrical field. Because in an electric current the positive and negative charges are moving at different speeds, relativity will affect the differently,"
  I think Lunar is correct in saying that particle physicists would consider the electric force as set up by virtual photons as only photons can move or react at the speed of light. I think it is the magnoflux that is causing the force.
CliveS
 

Offline daveshorts

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What flows in a magnetic field?
« Reply #7 on: 07/06/2010 12:35:31 »
Yes, the force in electromagnetism is carried by virtual photons in QED (Quantum Electro Dynamics) which travel at the speed of light.

What is magnoflux?
 

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What flows in a magnetic field?
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