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Author Topic: Magnet Myths and Misconceptions  (Read 605615 times)

TinselKoala

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Re: Magnet Myths and Misconceptions
« Reply #60 on: October 04, 2014, 10:20:59 PM »
Charge. It is the motion of charge, not of electrons themselves, that makes the field.

Electrons carry the unit negative charge, by definition and measurement, but as Qwert points out above the electrons themselves, for example in metal wires, don't need to move that fast. I think the situation with charge and moving electrons is kind of like "Newton's balls", where units of charge (the momentum of the "input ball") are transferred across the system very rapidly, even though the individual "balls" don't move hardly at all.
Magnetic fields can be produced by moving ions, both positive and negative. So it is the motion of the charge, not the motion of the charge +carriers+, that produces the field. Charge, motion, field: One thing. One.

OK, carry on.

Liberty

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Re: Magnet Myths and Misconceptions
« Reply #61 on: October 04, 2014, 10:53:31 PM »
Charge. It is the motion of charge, not of electrons themselves, that makes the field.

Electrons carry the unit negative charge, by definition and measurement, but as Qwert points out above the electrons themselves, for example in metal wires, don't need to move that fast. I think the situation with charge and moving electrons is kind of like "Newton's balls", where units of charge (the momentum of the "input ball") are transferred across the system very rapidly, even though the individual "balls" don't move hardly at all.
Magnetic fields can be produced by moving ions, both positive and negative. So it is the motion of the charge, not the motion of the charge +carriers+, that produces the field. Charge, motion, field: One thing. One.

OK, carry on.

So the movement of many charges (ions) in a magnet is what produces the continual magnetic field in a magnet?  Why can't these charges be depleted?

Liberty

MileHigh

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Re: Magnet Myths and Misconceptions
« Reply #62 on: October 04, 2014, 11:48:13 PM »
Newton II:

Yes, we agree that a moving electron has a magnetic field that "moves" with it.  Note however that I put "moves" in quotations.  The magnetic field does not literally move with the the electron.  What really happens is the moving electron changes the local magnetic field at every point in space around the moving electron as it moves.  In other words, if you are at a fixed point in space and an electron moves past you, you experience a changing magnetic field.   It's a subtle but important difference.

Think of sound waves.  A police car drives past you with the siren on.  You hear the siren first low, then very loud, and then low again.   The sound changes in volume as the police car passes you, but the sound is not literally "moving" with the police car.  The police car siren is emitting a fixed unmoving sound at every instant in time.  This is a continuous process.  Think of a boat moving through the water as another example.  The moving electron causes a "local disturbance" in the magnetic field.

When the moving electrons stop the energy contained in the magnetic field has to go somewhere.  In most cases the electrons move past the "stop point" because of the electrical inertia associated with the whole process.  That's the high-voltage spike.  It does not necessarily mean that the energy will become an EM wave.

Quote
In mechanics a solid mass 'm'  moving with velocity 'v' develops  kinetic energy  of  ½ mv2.   But when you supply energy to the electrons by applying voltage, the electron  cannot store energy in the form of   ½ mv2  because its mass is negligible.  So it creates a magnetic field to store the supplied energy.   When electrons are stopped, energy is released as EM wave.

There is a direct correspondence.  Mechanical inertia is mass x velocity.  Electrical inertia is inductance x current flow.  So for an inductor with current flowing through it, the magnetic flux generated is effectively the electrical inertia.  Think of this:  You energize an inductor and put energy into it by applying (voltage x current x time).  That creates a magnetic field.  The current flow and the magnetic field are directly related to each other  (current flow -> magnetic field).  So if you try to stop the current flow then the magnetic field "takes over" to induce the current flow (magnetic filed -> current flow.)  They are so closely related that one becomes the other and vice-versa.

TK:

There are a lot of misunderstandings about electric fields and charge also.  In a generator, there is no "charge" in the wires.  There is an induced electric field that pushes the electrons through the wires, without any net charge in the wires themselves.  Likewise, some people talk about voltage being related to charge density, but that's only for static electricity.  You have voltage in the windings of a generator with no excess charge density.  There are two sources of an electric field, the static electric field associated with electrostatics, and the "dynamic" electric field associated with changing magnetic fields.  A so-so analogy for current flow in a wire because of a dynamically induced electric field might be a simple vertical shaft with balls falling through a gravity field.  The gravity field is like the electric field and the balls are like the electrons.

Liberty:

The source of the magnetic field in a magnet is the trillions and trillions of electrons orbiting iron atoms where they are all orbiting in the same rotational direction.  Each one acts like a little tiny magnet.  The electrons spinning in tight little circles still create a magnetic field in the same way that an electron creates a magnetic field when moving in a straight line.

MileHigh

Pirate88179

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Re: Magnet Myths and Misconceptions
« Reply #63 on: October 05, 2014, 02:54:31 AM »
I have a question.  If you have a piece of 12ga. copper wire that has been used in operation with heavy currents (not over the wire's rated capacity though) for say 50 years.  If you take a new piece of the same ga. wire and compare the two...is there any differences that can be observed from the years of electron "movement" or "vibrations" in the old wire vs. the new?  In other words, and I am not talking about the elements degrading the insulation, or anything associated with over heating of the old wire, is there any chemical or physical change in the wire, like density, or any other change as a result of the electron movement in it for all of those years?

I have heard electricians use the term that an old wire was "worn out" and he was not talking about the insulation as it was bare copper wire.  What does this mean?  And, is it a result of electron movement causing degradation of the molecules in the copper wire?  Or, under a powerful electron microscope, would we see no changes in the old, used wire vs the new wire?  Does the old wire's resistance increase somehow over time and the resulting heating cause this degradation?  If so, what changes occur in the wire to cause it's resistance to increase?

Thanks, I am learning a lot in this topic thus far.

Bill

Newton II

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Re: Magnet Myths and Misconceptions
« Reply #64 on: October 05, 2014, 04:49:28 AM »
Why can't these charges be depleted?
Liberty


I think that is a great question.

In mechanics, the kinetic energy of a moving mass is defined as  "energy possessed by virtue of its velocity" and its magnitude is 1/2mv2

And potential energy of same mass is defined as "energy possessed by virtue of its position" and its magnitude is 'mgh'  where 'h' is its height above the ground. (reference)

So, when magnetic field produced by a moving charge is analogous to kinectic energy,  the static charge should be analogous to potential energy.

A  moving charge looses its kinetic energy which is magnetic field, when the charge is stopped. But it will still have potential energy in the form of electric charge.  This potential energy will be lost only if this charge literally 'falls' on the reference which is responsible for imparting potential energy on it.

The question here is,  a charge possesses potential energy with reference to what?  and who imparts it potential energy by  'lifting'  it above the reference?

I think this question is being dealt with in quantum mechanics since the very birth of quantum mechanics.  Don't know whether 'quantum mechanists'  have got the answer yet.

If this question is answered we will know the secret of this universe.

And it will be a revelation of 100G where 'G' stands for God.

Qwert

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Re: Magnet Myths and Misconceptions
« Reply #65 on: October 05, 2014, 09:59:12 AM »
And it will be a revelation of 100G where 'G' stands for God.
I guess a good example to understand the concept of moving charge at DC while electrons only push their neighbors is the known "domino effect" where domino pieces represent electrons: they need only small movement to transfer energy along their path: more rows have more energy, also taller pieces have more energy: one stands for I, another one for V.

vineet_kiran

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Re: Magnet Myths and Misconceptions
« Reply #66 on: October 05, 2014, 02:02:08 PM »
Strength of magnetic field produced by a coil depends on number turns also. 
 
Think that you have a superconductor wire at room temperature.  Make a coil with it having 'X' number of turns. Pass a DC of 'Y' amperes through it applying a voltage of 'Z'. The power input to the coil is 'YZ' watts.  Hence energy stored in magnetic field is also 'YZ' watts because coil is superconducting and no losses.
 
1) When number of turns is 'X',  input power is YZ and power of magnetic field is also YZ
 
2) Increase number of turns to '10X' adding additional wire, input power is 'YZ' and power of magnetic field is '10YZ'
 
3) Increase number of turns to '100X',  input power is 'YZ' and power of magnetic field is '100YZ'
 
4) Increase number of turns to 'infinite X',  input power is YZ and power of magnetic field is infinite!!  (coil is superconducting hence
    no resistance even with infinite turns)

 
Confusing....???? :-[

 

poynt99

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Re: Magnet Myths and Misconceptions
« Reply #67 on: October 05, 2014, 02:35:23 PM »
Bill,

I don't believe there is any physical change in the wire from extended use. Sounds like a myth if some are saying there is.

poynt99

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Re: Magnet Myths and Misconceptions
« Reply #68 on: October 05, 2014, 02:40:39 PM »
Strength of magnetic field produced by a coil depends on number turns also. 

That's academic, but what causes the field in a straight piece of wire?

Is it caused by the movement of the drift (free) electrons or the electron cloud in each atom? Or is it the alignment of the individual electrons to all "spin" with their axis' in the same plane?

vineet_kiran

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Re: Magnet Myths and Misconceptions
« Reply #69 on: October 05, 2014, 04:46:46 PM »
That's academic, but what causes the field in a straight piece of wire?

Is it caused by the movement of the drift (free) electrons or the electron cloud in each atom? Or is it the alignment of the individual electrons to all "spin" with their axis' in the same plane?


May be it is same as the case of schrodinger's cat, dead and alive at the same time depending on circumstances  because for DC, electrons have to move but for AC,  electrons only have to vibrate in tune with the changing magnetic field causing vibration.

Don't know the exact reason. Some knowledgeable person has to explain.


Pirate88179

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Re: Magnet Myths and Misconceptions
« Reply #70 on: October 05, 2014, 04:53:47 PM »
Bill,

I don't believe there is any physical change in the wire from extended use. Sounds like a myth if some are saying there is.

Thanks.  So, any change in the wire was due to external exposure to the elements and not any internal molecular change due to the movement/vibration of electrons.  Would this mean that the electrons move/vibrate in the empty space between the atoms that make up the copper and therefore have no effect on them?  Would it be like hitting a long pipe with a hammer and having the sound vibrations moving along the pipe from end to end?  I am having trouble visualizing this.  So then, the magnetic field surrounding a wire with moving/vibrating electrons is due to the electrons themselves aligning together to create the field and not the atoms of the copper conductor itself being manipulated in any way?  Then this would make the copper conductor an inert host to the activity of the electrons I suppose.

Now I find it harder to understand, if there is no interaction with the conductors atoms, then why do some materials act as conductors and some insulators?  If these vibrations occur in the empty space in the structure of the material then it should not matter what that material is, but we all know that it does.  Materials that make good conductors of electricity, as we all know, make good conductors of heat as well.  This would make me think that the molecular structure of the conductor material is important, but if the electron activity within the conductor has no interaction with the atoms of the material itself, then why would this be?

I just went through all of my electronics books over here where they discuss atomic structure, electrons, conductors and insulators, and I could not find any answer for this.

Thanks,

Bill

poynt99

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Re: Magnet Myths and Misconceptions
« Reply #71 on: October 05, 2014, 05:06:10 PM »
Bill,

Metals are good conductors because they exhibit free (loosely bound) electrons in their structure. Insulators don't have free electrons, so they are poor conductors of electricity.

See this pdf and this Hyperphysics page.

Just because the free electrons in a wire are constantly scattered and colliding as they make their way from one end to the other, doesn't mean the wire becomes worn out. For the electrons that do leave the wire, there are an equal number entering.

SeaMonkey

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Re: Magnet Myths and Misconceptions
« Reply #72 on: October 05, 2014, 06:38:40 PM »
Quote from: poynt99
I don't believe there is any physical change in the wire from extended use. Sounds like a myth if some are saying there is.

That's one I've not heard.

Although, it is reported that 'work hardened' copper is not
as conductive as freshly annealed soft copper.

TinselKoala

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Re: Magnet Myths and Misconceptions
« Reply #73 on: October 05, 2014, 06:57:30 PM »
(snip)
TK:

There are a lot of misunderstandings about electric fields and charge also.  In a generator, there is no "charge" in the wires.  There is an induced electric field that pushes the electrons through the wires, without any net charge in the wires themselves.  Likewise, some people talk about voltage being related to charge density, but that's only for static electricity.  You have voltage in the windings of a generator with no excess charge density.  There are two sources of an electric field, the static electric field associated with electrostatics, and the "dynamic" electric field associated with changing magnetic fields.  A so-so analogy for current flow in a wire because of a dynamically induced electric field might be a simple vertical shaft with balls falling through a gravity field.  The gravity field is like the electric field and the balls are like the electrons.

(snip)
MileHigh
Ah... er.... um.... almost.
There is only one field, the EM field. It is the relationship between charge and motion.  There is no difference between a "static" electrical field as in "electrostatics" and the "dynamic"  electric field associated with changing magnetic fields. A generator does in fact separate charge and in a current-carrying wire, charge is indeed separated. Don't believe me? Connect a capacitor across the output of your DC generator and watch what happens.
The changing magnetic field in the generator produces a movement of charge. What happens in the wire that is distant from the changing fields in the generator? The charge pressure that is created by the generator "pushing" on local charges in the wire is transferred -- like charge repels like -- down the wire and at the distal end you see a voltage: charge pressure.
The main differences between "electrostatic" charge and "dynamic" charge (current) are the number of charges involved and whether they are moving or not. A Coulomb is a _huge_ amount of charge. Put a Coulomb of charge onto something where it will be retained and you will have huge electric field effects associated with it. Make that thing smaller and the charge density will increase: voltage increases: until it leaks off due to isolation breakdown and conduction. Put a Coulomb of charge through a conductor every second, and you have one Ampere of current flowing and a large magnetic field associated with it. Flow that current into a capacitor and watch the charge pressure accumulate (voltage on the cap rises). Same field, same pressure, same voltage phenomena, whether "electrostatic" or "dynamic".
You can have currents that consist of beams of electrons in free space, as in Cathode Ray tubes. You can have currents that are transferred by conductive plasmas of ions, as in neon tubes. You can even have currents transferred by large ions dissolved in fluids, as in electrophoresis. But in each case it is the _charge_ that is moved by external fields (which result in the charge pressure gradient, AKA potential, AKA tension, AKA voltage), and which drags whatever material carrier along with it.

bboj

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Re: Magnet Myths and Misconceptions
« Reply #74 on: October 05, 2014, 07:01:46 PM »
And what is a charge?