The Naked Scientists

The Naked Scientists Forum

Author Topic: The field around a wire carrying a current  (Read 8990 times)

Offline McQueen

  • Hero Member
  • *****
  • Posts: 545
  • Thanked: 6 times
    • View Profile
    • http://www.geocities.com/natureoflight/pgindex
The field around a wire carrying a current
« on: 22/06/2005 20:06:26 »
Does our science lack objectivity ?  This is a question of vital importance  and too often it is one that is  thrust to one side and avoided. What do I mean by objectivity ? Well let us consider for instance the subject of electricity , an area of study which affects in one way or another  almost every branch of  physics and a large part of chemistry. The Laws of Electricity which we so diligently ( and successfully ) apply today were for the most part formulated by Andre Ampere (b.1775 d. 1836) , Hans Christian Oersted (b. 1771 d. 1851)  and Charles Augustin Coulomb (b. 1736 d.1806 ). What do these dates tell of the state of knowledge which existed at the time of the existence of  these undoubtedly great scientists :-

1)   During the period in which the above named scientists , Coulomb , Ampere and Oersted , lived ( mid 1750’s to the mid 1850’s) electricity was unknown , London was illuminated by Gas light , while the majority of the cities and towns of  the world still depended on oil lamps with wicks or candles.
2)   The atom had not yet been discovered nor was it perceived as the fundamental building block.
3)   The structure of the atom had not been discovered..
4)   The electron had not been discovered , or named , nor its existence even proposed.
5)   The photon had not even been conceived of , its suspected existence was still a half century away and its final acceptance and naming would take another half century.

   This is obviously an extremely abbreviated and fundamental list of what was not known at the time , a more comprehensive list would probably end up as big as the Encyclopaedia Brittanica.
    The obvious thought  in everyone’s mind at this stage is  : “Why is he making such a big deal of this , everything we have learnt from Coulomb , Ampere and Oersted has been repeatedly proven  over the ages. “
       To be te frank , the reason I have taken such a hard line is because  I wish to make an observation on certain facts which have been( unknowingly ) misrepresented by the above gentlemen and which have been perpetuated to this day , To this end I have had to demonstrate that , because of the dearth of knowledge , prevalent at the time , even these venerated men of science could be wrong. For instance if anyone were to enter the Naked Scientist forum and ask questions on whether on not atoms or electrons existed , they would be treated to wide spread derision and contempt.
       The premise which I wish to question is one that effects every aspects of physics , it concerns the shape of  a magnetic field around a straight wire carrying a current. .
    Ampére and Oersted both working in the in the mid-nineteenth century came up with the following observations after performing a number of experiments which demonstrated  that a moving charge exerted a force on a permanent magnet and that as Newton's third law predicted, the opposite was also true, that a magnet exerted a force on a moving charge:-
1)   the force is proportional to the magnitude and sign of the charge on the particle
2)   the force is proportional to the velocity of the charged particle
3)   the force is proportional to the magnitude of the magnetic field
4)   the magnitude of the force depends on the relative orientation between the line of flight and the direction of the magnetic field
5)   and the force always acts perpendicularly to the particle's line of flight.
The last statement is the least expected, since normally forces  act in the same direction as the field. For instance if you take the North and south poles of two bar magnets you will find that the force exerted is in the direction of the field , similarly the field in between the plates of a capacitor acts in the direction of the field.  Mathematically it is almost impossible to get a force which is perpendicular to the field unless highly unlikely steps such as cross multiplication of vectors is resorted to.   Henri Lorentz had managed to do this giving rise to what is  today known  as the Lorentz force . It is the force exerted by a moving charge and is seen to always act perpendicular to the direction of the charge. What is wrong with this  is that  what Lorentz had done was  to simply express the statements , in  mathematical terms ,  that Oersted and Ampére had made with regard to the fact that the magnetic force always acts perpendicularly to the direction of the flow of electrons in a wire.  He didn’t question the fact of whether these observations were true or false. As has been pointed out this is in a sense contrived since experience shows that normally forces act in the same direction as the field. What we have to determine is whether this statement ( i.e. that the magnetic field is always at right angles to a straight wire carrying a current.) is valid. Ampere and Oersted had both stated that the magnetic force acts perpendicular to the electric field .Yet the truth is that in reality  it is never possible to measure or map the field around a straight conductor carrying a current ( or more accurately it was not possible for either Ampére or Oersted to do so with the limited equipment available in the mid-nineteenth century ) for the simple reason that a current flowing in a circuit is always  circular. So what Ampére and Oersted and later Lorentz  had done was to ignore the fact that the current flowing through the wire was also flowing through the source  (i.e battery ) and to view the current in the straight wire as the only current present , when mapping the  associated magnetic fields , and currents which they were measuring and that  therefore their conclusions were erroneous. In other words they had mapped part  of the circuit and had assumed they were dealing with the whole. This has left the disconcerting impression , an impression which has persisted for more than 150 years , that the magnetic fields of force seen around a straight conductor are merely floating in space around the conductor , and that these lines of magnetic force are a manifestation of the flow of electrons in the wire and that the lines of force do not flow through and around the conductor , which is actually the case but that they form loops perpendicular to the wire. The magnetic field that , Ampére and Oersted had in fact mapped  around a “straight” conductor carrying a current was therefore the field due to  a circular current. If one examines the field due to a circular or doughnut shaped magnet it is  identical to that seen around a straight conductor carrying a current. If one takes a horseshoe magnet and holds it with the two poles pointing upwards at a paper and sprinkle iron filings on the paper the shape of the field is identical to that around a wire carrying a current .(i.e  the iron filings form loops perpendicularto the magnetic poles. )
Thus if it had in fact been possible to measure and map the field around a straight conductor (i.e a straight wire through which a current was flowing which was not connected to a circuit. ) the field around it would be the same as that seen around a bar magnet. The lines of force would then be seen to flow through the conductor originating at the positive end , flowing through the body of the conductor and then exiting the conductor at the negative end and circling back in loops to the positive end.   This is a momentous statement , it is something like  seeing a rainbow in the sky or witnessing the aurora borealis , the fact is that the field around a straight conductor would be identical to that around a bar magnet.
This new manifestation of the shape of a magnetic field around a straight conductor would completely change everything that we have so far taken for granted about currents and magnetic fields.  For instance it would raise the question of why a current does not flow in a permanent  magnet even though the field around a straight wire and a bar magnet are (as demonstrated )identical. Also since a macroscopic current is not flowing within a magnet and the field of both a  magnet and a wire carrying a current are identical , how does the magnetic field originate in the two cases ? In short all these questions would have to be re-examined. Fundamental questions such as what is a current and  what is a magnetic field would have to find new answers and solutions.

« Last Edit: 22/06/2005 20:27:06 by McQueen »


 

Offline DoctorBeaver

  • Naked Science Forum GOD!
  • *******
  • Posts: 12656
  • Thanked: 3 times
  • A stitch in time would have confused Einstein.
    • View Profile
Re: The field around a wire carrying a current
« Reply #1 on: 23/06/2005 05:59:21 »
I'm not a physicist so I'm in no position to question the actual physics you refer to. I can, however, see what appears to be a flaw. Surely you can have a straight wire in a looped circuit that is far enough away from the opposite side that it would have no effect on it: e.g. if you ran a wire around the Indianapolis motor racing track & ran a small current through it. I appreciate that there would still be curves involved, but the radius would be so great as for them to be almost unnoticeable.
The question this brings to my mind is this - if you have a straight wire with a curve at each end, would the EM field be affected in a way proportionate to the radius of the curve? In other words, would a sharper curve have a more profound effect than a very gradual curve?

We learn from history that we do not learn from history.
(Georg Hegel)
 

Offline daveshorts

  • Moderator
  • Neilep Level Member
  • *****
  • Posts: 2583
  • Physics, Experiments
    • View Profile
    • http://www.chaosscience.org.uk
Re: The field around a wire carrying a current
« Reply #2 on: 23/06/2005 13:07:59 »
Sorry you are wrong, you can plot the field around a wire (admittedly in a large loop) using a compass - I have done it, the field goes in a circle around a wire.

The reason the field comes out of a magnet is that it is analagous to a solenoid not a straight wire - In a solenoid the field is going around all the wires in such a way that it goes in one end of the solenoid and out the other.

Part of the reason why magnetic field is so strange and behaves with all the right angles is that it isn't a force like gravity or the electric force, there are no magnetic monopoles, it is a relativistic correction to the electric force. This correction has been constructed in such a was as to look like the other fields as we know how to think about those.

There is a current flowing in a permenant magnet, the electrons are orbiting thier atoms, and in ferro-magnetic atoms some of these are orbiting in the same direction.
 

Offline McQueen

  • Hero Member
  • *****
  • Posts: 545
  • Thanked: 6 times
    • View Profile
    • http://www.geocities.com/natureoflight/pgindex
Re: The field around a wire carrying a current
« Reply #3 on: 23/06/2005 13:21:26 »
I'm not a physicist so I'm in no position to question the actual physics you refer to. I can, however, see what appears to be a flaw. Surely you can have a straight wire in a looped circuit that is far enough away from the opposite side that it would have no effect on it: e.g. if you ran a wire around the Indianapolis motor racing track & ran a small current through it. I appreciate that there would still be curves involved, but the radius would be so great as for them to be almost unnoticeable.
The question this brings to my mind is this - if you have a straight wire with a curve at each end, would the EM field be affected in a way proportionate to the radius of the curve? In other words, would a sharper curve have a more profound effect than a very gradual curve?

We learn from history that we do not learn from history.
(Georg Hegel)

Doctor Beaver

Theoretically it would not matter how big the loop were or how  slight the curves  involved , a current still has to flow around the circuit for a magnetic field to appear and the shape of that magnetic field  , manifesting itself in loops perpendicular to the wire , would be governed by the fact that a circular current is flowing through it . If you look back at my comparison of a magnetic field around a wire to that of a doughnut shaped magnet it should become evident that the size of the magnet involved would not matter.  The point that I am trying to make , and it is a vitally important point , as you will see later on , is that the magnetic field around a wire carrying a current and that due to a permanent magnet are identical in every respect . This is not accepted , the widely held view is that the shape of the magnetic field around a straight conductor is because it is due to the flow of electrons along a wire while the shape of the magnetic field around a bar magnet is due to the fact that its magnetic field is attributed to a different cause , namely the alignment of electron spin . Thus according to presently accepted wisdom , a flow of electrons results in the field consisting of loops perpendicular to the direction of the flow of electrons while aligned electron spin results in the field as observed around a bar magnet. I am trying to show using logic that this is erroneous and that if in fact it were possible to map the magnetic field around a straight wire which is not part of a circuit , the shape of the magnetic field would be identical to that around a bar magnet. This would completely change the accepted wisdom on magnetic fields and electric currents. I appreciate your amateur status viz-a viz physics , however that is of no great consequence  in the present instance , since this is more a question of applied logic than of any deep seated knowledge of physics.  To answer your second point , obviously , since electromagnetic fields interact , the radius of  curvature becomes important , the more sharply curved the wire the greater the interaction between the fields, which because they are flowing in the same direction are centred mainly within the curvature of the loop. The reason that the currents are flowing in the same direction is because they are part of a circuit or circle. The important thing to note is that the shape of the field is still exactly analogous to that around a permanent magnet. Thus if you had a doughnut or ring shaped magnet with a sharper radius of curvature , the field would be similarly concentrated in the center , however it must be assumed  that the magnetism of the doughnut shaped magnet would be along the axis of the doughnut  and not perpendicular to it.  
 

Offline McQueen

  • Hero Member
  • *****
  • Posts: 545
  • Thanked: 6 times
    • View Profile
    • http://www.geocities.com/natureoflight/pgindex
Re: The field around a wire carrying a current
« Reply #4 on: 23/06/2005 13:39:10 »
Daveshorts

Sorry you are wrong, you can plot the field around a wire (admittedly in a large loop) using a compass - I have done it, the field goes in a circle around a wire.

I can’t let this pass , I  have to say you are mistaken . It doesn’t matter how large you make your circle.  If you try to plot the field with a compass by laying your circuit flat on a piece of paper , you wil not be able to map a field. The correct way to map the field is to push the circle of wire vertically through the paper , the field will then be seen to consist of closed loops perpendicular to the wire.
 

Offline daveshorts

  • Moderator
  • Neilep Level Member
  • *****
  • Posts: 2583
  • Physics, Experiments
    • View Profile
    • http://www.chaosscience.org.uk
Re: The field around a wire carrying a current
« Reply #5 on: 23/06/2005 13:49:35 »
Urr that is what I did , the wire is vertical the paper flat and the compass moving around the paper. The field circles the wire and gets weaker as you move out, which is what you would expect from the Biot Savat law isn't it?
 

Offline gsmollin

  • Hero Member
  • *****
  • Posts: 749
    • View Profile
Re: The field around a wire carrying a current
« Reply #6 on: 23/06/2005 13:56:26 »
This whole discussion is missing the point of the magnetic field orientation at all points being orthogonal to the electric current; the moving point charge in a magnetic field experiences a force orthogonal to its velocity vector, even as that vector is curving due to the orthogonal force. This orthogonality is required by conservation of energy. If the force on the charge were not identically orthogonal, conservation of energy would be violated, and that does not happen, so it is orthogonal. This relationship does trace back to the lack of magnetic monopoles. Since they have not been observed, all magnetic field lines travel in circles, just like electric currents. There are no open ended electric currents, i.e., no infinite straight conductors, and there are no straight magnetic field lines.
 

Offline daveshorts

  • Moderator
  • Neilep Level Member
  • *****
  • Posts: 2583
  • Physics, Experiments
    • View Profile
    • http://www.chaosscience.org.uk
Re: The field around a wire carrying a current
« Reply #7 on: 23/06/2005 15:10:28 »
If the electric current is changing you can have non-circular electric currents, if you have a wire with a large metal sphere attached at either end and you apply an AC electric field you will get a small current with no return path
 

Offline McQueen

  • Hero Member
  • *****
  • Posts: 545
  • Thanked: 6 times
    • View Profile
    • http://www.geocities.com/natureoflight/pgindex
Re: The field around a wire carrying a current
« Reply #8 on: 23/06/2005 16:39:33 »
gsmollin
The whole point is that a force ordinarily acts in the direction  of the field not orthogonally to it. This whole concept of orthogonality has arisen out of the fact that a part of the circuit (i.e ., the straight wire ) has been attributed with properties which it does not possess . Namely that , a moving charge results in a magnetic field orthogonal to it . In truth the orthogonality of the field is due to the fact that the current is circular. A ring magnet or to take my earlier example a horse shoe magnet displays exactly the same type of field , orthogonal to the poles. There are no moving charges , ( apart from aligned electron spin ) in the magnet , yet the field is orthogonal in this case and different in the case of a bar magnet , how do you account for this ? An examination of the facts can only lead to the conclusion , that yes , the field around a wire does in fact resemble in every respect the field around a circular magnet . Yet the magnetism exhibited by a wire through which a current is flowing is attributed to one cause , the flow of electrons in the wire , while the field around a permanent magnet is attributed to another cause. This in itself is suspect attributing identical phenomenon to two different causative factors. Why is it so difficult to admit that the field around a wire ( loops emanating perpendicularly to the wire ) is due to the fact that the current in question is  always a circular current.  Or are you claiming the fact that the current is circular has nothing at all to do with the shape of the field around the wire and that it is solely due to the fact that the charges are moving ?
 

Offline gsmollin

  • Hero Member
  • *****
  • Posts: 749
    • View Profile
Re: The field around a wire carrying a current
« Reply #9 on: 23/06/2005 17:15:11 »
quote:
Originally posted by daveshorts

If the electric current is changing you can have non-circular electric currents, if you have a wire with a large metal sphere attached at either end and you apply an AC electric field you will get a small current with no return path



The return path is the displacement current that flows between the spheres in the space around the wire. I think Helmholtz, or Hertz did this experiment.
 

Offline gsmollin

  • Hero Member
  • *****
  • Posts: 749
    • View Profile
Re: The field around a wire carrying a current
« Reply #10 on: 23/06/2005 17:22:15 »
quote:
Originally posted by McQueen

gsmollin
The whole point is that a force ordinarily acts in the direction  of the field not orthogonally to it. This whole concept of orthogonality has arisen out of the fact that a part of the circuit (i.e ., the straight wire ) has been attributed with properties which it does not possess . Namely that , a moving charge results in a magnetic field orthogonal to it . In truth the orthogonality of the field is due to the fact that the current is circular. A ring magnet or to take my earlier example a horse shoe magnet displays exactly the same type of field , orthogonal to the poles. There are no moving charges , ( apart from aligned electron spin ) in the magnet , yet the field is orthogonal in this case and different in the case of a bar magnet , how do you account for this ? An examination of the facts can only lead to the conclusion , that yes , the field around a wire does in fact resemble in every respect the field around a circular magnet . Yet the magnetism exhibited by a wire through which a current is flowing is attributed to one cause , the flow of electrons in the wire , while the field around a permanent magnet is attributed to another cause. This in itself is suspect attributing identical phenomenon to two different causative factors. Why is it so difficult to admit that the field around a wire ( loops emanating perpendicularly to the wire ) is due to the fact that the current in question is  always a circular current.  Or are you claiming the fact that the current is circular has nothing at all to do with the shape of the field around the wire and that it is solely due to the fact that the charges are moving ?




My whole point is that there are two fields, one stationary in the space surrounding the charge, and the other produced by the charge as it moves. Now we are looking at two magnetic fields, and they will react to each other in the usual way. This is why the force on the moving charge is orthogonal.

The "circular" bit may be getting confusing here. In there were an infinitly long, straight wire, or moving charges to that effect, then the magnetic field around it would be circular. I said above that currents always flowed in circles. I would like to correct that to say that they always flow in closed loops. Magnetic field lines also always form closed loops, but in the special case of an infinitly long conductor, they also form circles.
 

Offline McQueen

  • Hero Member
  • *****
  • Posts: 545
  • Thanked: 6 times
    • View Profile
    • http://www.geocities.com/natureoflight/pgindex
Re: The field around a wire carrying a current
« Reply #11 on: 23/06/2005 22:56:23 »
gsmollin
My whole point is that there are two fields, one stationary in the space surrounding the charge, and the other produced by the charge as it moves. Now we are looking at two magnetic fields, and they will react to each other in the usual way. This is why the force on the moving charge is orthogonal
.


Would you agree that a permanent magnet contains  only stationary charges , even if they are aligned to give a strong magnetic effect. There are no moving charges , in the sense of traveling electrons , in a permanent magnet , is that a given ? In other words there is only one field , the stationary field . Then why does the field around a horse shoe magnet exactly resemble the field around a wire carrying a current ? .  The field around the poles of such a magnet are orthogonal to the poles , in exactly the same manner as the field around a straight wire , which also in reality happens to be not straight but part of a circle.  Yet you have just stated that such a field is due to the complex interactions between stationary and moving magnetic fields.
Further coming back to the original gist of  the post , you must realize that when Ampere and Oersted formulated these laws , they had no idea of what a current was , and no inkling that such things as electrons even existed. It was not unreasonable for  them to assume that when they mapped the field around a straight wire , they assumed that the mapped field truly represented that around a straight wire , never realizing that the current was also flowing through the battery making a complete circle. Otherwise , I am sure the terminology field around a straight wire would never have been used. Furthermore if they had realized that the current was flowing in a circular path , it is probable that they would have immediately seen the similarity between the field around a circuit and that of a ring shaped magnet , since permanents magnets of all shapes were probably an indispensable part of the laboratory equipment of those days  (i.e late 1700 to early 1800’s ).
« Last Edit: 23/06/2005 23:18:44 by McQueen »
 

Offline daveshorts

  • Moderator
  • Neilep Level Member
  • *****
  • Posts: 2583
  • Physics, Experiments
    • View Profile
    • http://www.chaosscience.org.uk
Re: The field around a wire carrying a current
« Reply #12 on: 24/06/2005 02:13:45 »
In a permenant magnet there are lots of electrons that all have angular momentum in the same direction - if we make a slightly dodgy comparison with classical mechanics this means that there are loads of electrons going in little circles. The magnetic field from lots of little circles is the same as that form a current going round the edge - this is why the field from a permenant magnet is the same as a solenoid. So there are lots of moving charges so I don't agree.

Also the field from a loop of wire is in fact the same as an axially magnetised disc magnet not a ring shaped magnet.

ps Aaaah the thing about the displacement current does make sense, I should have paid more attention in some lectures, cheers
 

Offline gsmollin

  • Hero Member
  • *****
  • Posts: 749
    • View Profile
Re: The field around a wire carrying a current
« Reply #13 on: 24/06/2005 13:49:01 »
quote:
Originally posted by McQueen



Would you agree that a permanent magnet contains  only stationary charges , even if they are aligned to give a strong magnetic effect. There are no moving charges , in the sense of traveling electrons , in a permanent magnet , is that a given ? In other words there is only one field , the stationary field . Then why does the field around a horse shoe magnet exactly resemble the field around a wire carrying a current ? .  The field around the poles of such a magnet are orthogonal to the poles , in exactly the same manner as the field around a straight wire , which also in reality happens to be not straight but part of a circle.  Yet you have just stated that such a field is due to the complex interactions between stationary and moving magnetic fields.
Further coming back to the original gist of  the post , you must realize that when Ampere and Oersted formulated these laws , they had no idea of what a current was , and no inkling that such things as electrons even existed. It was not unreasonable for  them to assume that when they mapped the field around a straight wire , they assumed that the mapped field truly represented that around a straight wire , never realizing that the current was also flowing through the battery making a complete circle. Otherwise , I am sure the terminology field around a straight wire would never have been used. Furthermore if they had realized that the current was flowing in a circular path , it is probable that they would have immediately seen the similarity between the field around a circuit and that of a ring shaped magnet , since permanents magnets of all shapes were probably an indispensable part of the laboratory equipment of those days  (i.e late 1700 to early 1800’s ).




Stationary electric charges do not produce magnetic fields. We can verify that with many kinds of experiments involving electric currents. So, it is NOT given that a permanent magnet has only stationary charges. We know that the charges in materials are in motion, and that moving charges produce magnetic fields, so it is now known that permanent magnets are produced by moving charges in the permanent magnetic material. The QM characteristics of the moving charges does not even need to be invoked.

I also do not agree that the field lines from a permanent magnet are orthogonal to the poles, but perhaps a diagram of your claim would help. In a bar magnet, the lines come out through the north pole, and enter the south pole, completing the closed loop inside the bar magnet. To my mind, the lines are parallel to the poles of the magnet. If one drew a line orthogonal to the flux lines just outside the north pole of the bar magnet, it would be parallel to the pole face of the magnet. Is that what you are saying?

Actually, I really don't understand your claim. I think you need to state it more clearly, at least for me. Say, in 25 words or less.
« Last Edit: 24/06/2005 13:50:12 by gsmollin »
 

Offline McQueen

  • Hero Member
  • *****
  • Posts: 545
  • Thanked: 6 times
    • View Profile
    • http://www.geocities.com/natureoflight/pgindex
Re: The field around a wire carrying a current
« Reply #14 on: 26/06/2005 23:29:39 »
Gsmollin

I have been away for the week-end.  I will  try to be  brief. I suspect  my previous verbosity had to do with the audaciousness of the ideas I am trying to convey. What if ……electrical energy were conveyed by photons and not by electrons ?
Present wisdom states that according to the PEP free electrons or electrons in the outer orbits cannot emit or absorb photons because of their inability to cope with the forces of recoil , unless ………. the emitted photon does not violate the  HUP (i.e it is re-absorbed almost immediately.) .  This explains how magnetic fields are formed , because the electrons emitting photons need to immediately re-absorb a photon of exactly the same frequency that they emitted , and the same applies to photons (i.e., they need to reach an electron lacking exactly the same amount of energy} the electrons in the conductor being the nearest source of such electrons , the photons loop back to re-enter the conductor at the nearest point , which because of the dynamic forces within the conductor , often means they  have to loop back to the nearest point of entry into the conductor. This scenario explains everything : The existence of fields real enough to deflect compass needles and result in patterns of iron filings ,back EMF , magnetic fields , electromagnetic fields etc., in a seamless manner . Doing away with multiple explanations for the same phenomena.
P.S You are right the magnetic field lines around a bar magnet run parallel to it , if however you bend the bar magnet so that it resembles a horse shoe , then the field lines become orthogonal to the poles , resembling those of a wire carrying a current and I suspect for the same reason.
« Last Edit: 26/06/2005 23:37:13 by McQueen »
 

Offline gsmollin

  • Hero Member
  • *****
  • Posts: 749
    • View Profile
Re: The field around a wire carrying a current
« Reply #15 on: 28/06/2005 05:15:16 »
OK, I think what you are saying is the same as the theory of quantum mechanics. The magnetic field is transmitted by virtual photons. All electromagnetic phenomena are caused by the exchange of virtual photons.

I don't know about the looping back around bit, however. There may be something here, I'm just not understanding it enough to say. Since virtual photons are massless, they can transmit a force with infinite range, so they could move in a loop when transmitting magnetic fields. A loop is no more infinite than a straight line.

Actually, I just don't know enough about the characteristics of virtual photons to say yes or no to this. While I accept the concept of virtual photons, as part of QM, I do so only because it is inevitable to explain semiconductor physics. I have not studied their properties enough to comment on this. Maybe somebody else can help.

P.S. If you bend a bar magnet into a U, or a horseshoe, or any curve, the magnetic field lines will prescribe a curve tangent to the curvature of the bent magnet. They will still exit at the north pole, and reenter the magnet at the south pole. I don't see any change to the field's behavior in this example.
« Last Edit: 28/06/2005 05:19:23 by gsmollin »
 

Offline McQueen

  • Hero Member
  • *****
  • Posts: 545
  • Thanked: 6 times
    • View Profile
    • http://www.geocities.com/natureoflight/pgindex
Re: The field around a wire carrying a current
« Reply #16 on: 28/06/2005 22:07:17 »
Gsmollin
OK, I think what you are saying is the same as the theory of quantum mechanics. The magnetic field is transmitted by virtual photons. All electromagnetic phenomena are caused by the exchange of virtual photons.

I am aware of this theory but again it is just nitpicking in a sense , if virtual photons are responsible for the propagation of electrical forces , why can’t real photons be involved ? It comes down to the Pauli Exclusion Principle  and the inability of free electrons to deal with the forces of recoil. The point I am trying to make is that it is precisely in dealing with the PEP that lines of force arise. Whereas the theory advanced by QM is that “Lines of force “ are due to virtual photons. While one can accept that virtual photons might conceivably have the power to alter an electrons direction of motion it is highly unlikely , by definition , that they can contribute anything to either its velocity or energy , something which would have to happen if energy is to be conveyed. Again if one studies the manner in which light propagates through glass it is through the absorption and emission of photons on their passage through the glass by electrons . In what way does this make sense , light can be propagated , light (i.e., electromagnetic radiation ) can propagate through glass through the absorption and emission of photons but electrical energy is propagated through virtual photons ?

They will still exit at the north pole, and reenter the magnet at the south pole. I don't see any change to the field's behavior in this example.

It is fairly easy to get hold of as horseshoe magnet and some iron filings , if you hold the magnet so that the poles are vertical , place a paper horizontally across the poles and sprinkle some iron filings on the paper the difference in the field formation will be apparent.
 

The Naked Scientists Forum

Re: The field around a wire carrying a current
« Reply #16 on: 28/06/2005 22:07:17 »

 

SMF 2.0.10 | SMF © 2015, Simple Machines
SMFAds for Free Forums