Stupid question relating to electric induction

[atommo]

Hi,

I've been interested in the science behind electrons/magnetism for quite a while. I've been learning quite a bit from various sources online. However there is one thing that's really nagging me.

Magnetic fields result from moving electrons. That indicates that a permanent magnet has electrons inside it moving in a circular fashion to produce poles (essentially an electromagnet but the material itself retains that flow).

Now the thing that I'm wondering about is this: You can put an iron core inside a copper coil- run electricity through the coil and you induce a magnetic field in the iron (by causing the electrons in the iron to get dragged along by the current in the copper coil in that same direction).

Now, if you put a permanent magnet in the copper coil, would it cause any form of current to flow in the coil (even if only slightly)? I know that people say no movement = no energy, but a permanent magnet DOES contain energy (the electrons in it that are causing it to have a magnetic field in the first place).

This is all under the assumption that permanent magnets contain a type of internal electron flow in a circular fashion (I don't see how a field could be produced without moving electrons)

Something isn't adding up so hopefully someone could explain.

I know this is probably a stupid question but I'm really curious.

Thanks

 

[Merlin3189]

You're pretty near with this.
If you put a permanent magnet into a coil, you will get a pulse of current, but it will quickly die away when the magnet stays inside the coil.
You get another pulse of current when you remove the magnet.

Michael Faraday realized that you generate an emf and current only when the magnetic field is changing. The emf is proportional to the rate of change of magnetic flux linked to the coil.

With two adjacent coils one will induce current in the other only when its current is changing and producing a changing magnetic field. That's why transformers work only with AC.

 

[BvU]

Now, if you put a permanent magnet in the copper coil, would it cause any form of current to flow in the coil

No, in the same way you don't get current in an outer coil if there is an smaller coil inside that has DC current circulating. Only when the current is switched on (or off) you get a pulse. Try it !

 

[Merlin3189]

... You can put an iron core inside a copper coil- run electricity through the coil and you induce a magnetic field in the iron (by causing the electrons in the iron to get dragged along by the current in the copper coil in that same direction).

I think it is more like: the electrons in the iron are bound to the atoms, but already orbiting and therefore having a magnetic field, but the magnets are randomly oriented. When you apply the current to the coil, this creates a magnetic field and causes the iron atoms to align in the same direction. Then their effects add up to give a macroscopic magnetic field.

That is not an accurate description, because it is really a rough description of paramagnetism rather than ferromagnetism. Ferromagnetism is a much stronger effect involving large groups of atoms - domains - where the atomic fields are already aligned. When the random alignment of the domains becomes organised by the external field, their macroscopic field is much stronger and may also persist when the current is removed.

 

[atommo]

I kind of get that but I still don't fully understand why.

If the above is an electron moving towards the screen then the magnetic field it produces would be counterclockwise according to the right hand rule.

Using that logic, see below:

Green is copper wire, blue is electron movement in a permanent magnet and purple is the magnetic field.
I always picture a permanent magnet as having its own self-contained electric current as I don't know how they would produce a field otherwise, hence you see the electron flow inside the permanent magnet flowing counterclockwise. This produces the purple magnetic field. However this magnetic field would in theory envelop the copper coil surrounding it. If the magnetic field direction surrounding the electrons in the wire is stronger on one side, wouldn't it cause the electrons in said wire to also flow?

See picture above. If the big purple arrow (going up) of magnetic field is caused by something external, wouldn't it cause the other side of the electron's field to go down and cause the electron to move toward the screen?

That is what is confusing me a lot

 

[atommo]

The only (probably wrong) explanation I can think of as to why they only seem to interact when there is physical motion involved is when both are unchanging in state and position (even if such a state involves electrons flowing), an electron's own field will overcome any external field no matter how strong, a bit like if each electron became its own superconductor, and that state can only be broken by making the external field 'collide' with the electron to break that state. It just doesn't seem right.

 

[sophiecentaur]

@atommo You may be trying to understand this by using your own terms alone. They may not be appropriate for you to get the right answers.
Am emf is induced by a varying current or Magnetic field.No change, no emf.
If you have googled electromagnetic induction you will have seen many diagrams along the lines of yours but the details may be different. Look at those diagrams and read the words that accompany them. (Several times and in detail, without skimming). I could give you exactly the same story and the same diagram but why - when it's available all over the Internet?
Do not rely on just one source - it could actually be wrong. Several sources can be used to check each other. The Hyperphysics is a good source for all this basic stuff. Try it.

 

[atommo]

I have seen diagrams like what I've shown and they say that if electricity ran through the coil it would enhance the effect of the magnet, but didn't say if any current would flow in the coil when external power was not applied. I think I'll have to try and set up an experiment if I can acquire the parts.

Thanks for the responses!

 

[sophiecentaur]

but didn't say if any current would flow in the coil when external power was not applied.

I don't know what you read but any information about electromagnetic induction will include the fact that the Field has to be changing. The magnetic field will be there for all non-zero currents, whether changing or not- so the situations are not reciprocal.

I repeat my comment that you should read more and more. and it is essential not to stop half way through what you are reading because you think you have taken it all on board. This is a problem that we can all have - we start 'arguing' in our heads with what we are reading and don't read to the end. First lesson is that it has all been sorted out (to that level of knowledge at any rate) and that the standard explanations are 1. Complete and 2. Consistent with what we can observe.

 

[atommo]

That is very true but at the same time I feel like I need to see/experience it first-hand to fully accept it

 

[Merlin3189]

I think your diagrams have an error: the current flows in the opposite direction to the electrons. So your "towards" diagram has the field reversed. This follows on in your main diagram.

 

[anorlunda]

This is all under the assumption that permanent magnets contain a type of internal electron flow in a circular fashion (I don't see how a field could be produced without moving electrons)

I always picture a permanent magnet as having its own self-contained electric current as I don't know how they would produce a field otherwise,

That's wrong, and it may lie at the root of your misunderstandings. There are no currents in a permanent magnet just sitting there. We require members to do some of their own study before posting questions here. In this case, I'll give you a start. Read and understand this: https://en.wikipedia.org/wiki/Magnetism#Sources_of_magnetism

 

[atommo]

I think your diagrams have an error: the current flows in the opposite direction to the electrons. So your "towards" diagram has the field reversed.

Good spot- the green positive and negative symbols should have been swapped around. I think everything else was as I intended it though. Sorry if that led to any confusion

That's wrong, and it may lie at the root of your misunderstandings. There are no currents in a permanent magnet just sitting there. We require members to do some of their own study before posting questions here.

Savage but fair enough.

This was what gave me the idea of self-conatined electron flow within a magnet: https://www.falstad.com/vector3dm/

The way it shows it makes me imagine electrons going round in circles within the magnet

 

[sophiecentaur]

That is very true but at the same time I feel like I need to see/experience it first-hand to fully accept it

How many really interesting and important phenomena would satisfy that requirement? You cannot 'see' electrons, you cannot identify a single atomic energy transition by looking, you cannot feel individual molecules moving through a gas. I think you are confused between familiarity with an idea and with personal experiences.
Reading a book / website is about the closest we can hope for in most of our experiences of Science. If we are lucky, we may do a few experiments on our own but, people who try random experiments without some good direction tend to walk away with nothing.
Science is referred to as a 'discipline' with good reason.

 

[BvU]

This was what gave me the idea of self-conatined electron flow within a magnet: https://www.falstad.com/vector3dm/

The way it shows it makes me imagine electrons going round in circles within the magnet

That is definitely not what the accompanying text says !
You got carried away by your imagination and forgot to check the basics.

 

[gmax137]

Reading a book / website is about the closest we can hope for in most of our experiences of Science. If we are lucky, we may do a few experiments on our own but, people who try random experiments without some good direction tend to walk away with nothing.

I think I understand what you're getting at here, but still there are lots of "experiments" that any of us can do that are very instructive. In this case, the OP could wire up a coil and a voltmeter; then see for himself that pushing a magnet into the coil causes the needle to jump, and also that the needle returns to zero when he stops moving the magnet. Seeing is believing, etc.

I had this same thought (simple experiment / demonstrations) when reading a recent thread on momentum & energy in collisions. When I was in school, we did all these things on air tables to bring the words home. I think trying to learn basic physics by reading books, without demonstrations, is a tough way to go.

 

[sophiecentaur]

“Seeing is believing” but not when it’s Penn and Teller showing you.
There are plenty of examples where seeing can lead you to the wrong conclusion.
You have to be so careful about the validity of evidence.

 

[gmax137]

You are quite right, this part of your post is very important to keep in mind:

random experiments without some good direction

Careful experiments, with good notes. And no jumping to conclusions.

 

[Charles Link]

For magnetic surface currents in a permanent magnet see: http://farside.ph.utexas.edu/teaching/302l/lectures/node77.html $\\$ See also a Physics Forums Insights article that I authored: https://www.physicsforums.com/insights/permanent-magnets-ferromagnetism-magnetic-surface-currents/ $\\$ Some very detailed calculations have shown these magnetic surface currents to be a theory having considerable merit. The magnetic surface currents, along with Biot-Savart's law give results for the magnetic field that are completely consistent with the magnetic pole model for the magnetic field that is computed. $\\$ Griffiths' E&M textbook also presents them in chapter 6. His derivation is rather advanced and is easily overlooked by physics students who study his book, because he doesn't emphasize in great detail the results of his derivation, which I think are quite important in explaining the magnetic field of a permanent magnet.

 

[atommo]

I just have some very strange things I want to try and I learn best by visualising!

For example I know that the electromagnetic force is caused by (virtual) photons emitted by Fermions (normally electrons in examples) which then interact with other Fermions in a way which either repels or attracts based on the wave-type (atleast that's the basic gist of what I get). I just find it hard to imagine the electrons are not really traveling inside a permanent magnet. All my understanding points to magnetic force happening as a result of the movement of electrons (or any Fermion for that matter).

From what has been explained here there is a fundamental difference between an electromagnet and a permanent magnet (electromagnets use current whereas permanent magnets use magnetic moment alignment..?)

Whereas I was under the impression permanent magnets had a self-contained current of their own which was inside the magnetic material itself- I thought the material acted in such a way as to allow for such a condition for a long period of time (and the act of taking a hammer or something of the like to it caused the material to go out of alignment which is what caused it to lose the magnetism/current).

I even visualise a magnet attracting some unmagnetised iron as the magnet causing the iron electrons to align and circulate at the same speed as the magnet, creating a magnetic field of equal strength and then attracting. See below for how I thought the magnetic fields and electron movement interlinked

 

[Charles Link]

I just have some very strange things I want to try and I learn best by visualising!

For example I know that the electromagnetic force is caused by (virtual) photons emitted by Fermions (normally electrons in examples) which then interact with other Fermions in a way which either repels or attracts based on the wave-type (atleast that's the basic gist of what I get). I just find it hard to imagine the electrons are not really traveling inside a permanent magnet. All my understanding points to magnetic force happening as a result of the movement of electrons (or any Fermion for that matter).

From what has been explained here there is a fundamental difference between an electromagnet and a permanent magnet (electromagnets use current whereas permanent magnets use magnetic moment alignment..?)

Whereas I was under the impression permanent magnets had a self-contained current of their own which was inside the magnetic material itself- I thought the material acted in such a way as to allow for such a condition for a long period of time (and the act of taking a hammer or something of the like to it caused the material to go out of alignment which is what caused it to lose the magnetism/current).

I even visualise a magnet attracting some unmagnetised iron as the magnet causing the iron electrons to align and circulate at the same speed as the magnet, creating a magnetic field of equal strength and then attracting. See below for how I thought the magnetic fields and electron movement interlinked

View attachment 236038

Please see my post 19.

 

[atommo]

For magnetic surface currents in a permanent magnet see: http://farside.ph.utexas.edu/teaching/302l/lectures/node77.html $\\$ See also a Physics Forums Insights article that I authored: https://www.physicsforums.com/insights/permanent-magnets-ferromagnetism-magnetic-surface-currents/ $\\$ Some very detailed calculations have shown these magnetic surface currents to be a theory having considerable merit. The magnetic surface currents, along with Biot-Savart's law give results for the magnetic field that are completely consistent with the magnetic pole model for the magnetic field that is computed. $\\$ Griffiths' E&M textbook also presents them in chapter 6. His derivation is rather advanced and is easily overlooked by physics students who study his book, because he doesn't emphasize in great detail the results of his derivation, which I think are quite important in explaining the magnetic field of a permanent magnet.

I think that was exactly what I was wanting! Explains in an easy-to-visualise way and I think I get it now. That makes a lot more sense. So I wasn't entirely wrong; there is an electric current. Its just exclusively on the very outside of the material.

Thank you!

 

[Charles Link]

I think that was exactly what I was wanting! Explains in an easy-to-visualise way and I think I get it now. That makes a lot more sense. So I wasn't entirely wrong; there is an electric current. Its just exclusively on the very outside of the material.

Thank you!

It's actually a different kind of current in that there is no actual electrical charge transport occurring. It is impossible to measure this current with a current meter, but all the calculations that are done regarding this "bound current" are extremely consistent. $\\$ On another note, this is actually extremely useful in this sense. In a transformer, plastic laminations are usually included to block unwanted "eddy currents" that occur. The "bound" magnetic surface currents are not blocked by these laminations, so that the magnetic field of the transformer does just what it is supposed to. If the laminations were to block the magnetic surface currents, the magnetic field of the transformer would be greatly reduced by the laminations.

 

[atommo]

That's really interesting. The next nagging question on my mind is what if you physically rotate the magnet in the direction its 'virtual current' is traveling in? Would that turn it into an actual current since you would be doing the act of physically rotating the magnet, thus the electrons too?

This is what I'm tempted to set up an experiment for. I get a coil, put a rod magnet inside it, attach both ends of the coil to a voltmeter, attach one pole of the magnet to the end of a drill and then turn the drill on. The magnet will rotate and I wonder if the voltmeter will read a current...

 

[sophiecentaur]

For example I know that the electromagnetic force is caused by (virtual) photons emitted by Fermions (normally electrons in examples) which then interact with other Fermions in a way which either repels or attracts based on the wave-type (atleast that's the basic gist of what I get). I just find it hard to imagine the electrons are not really traveling inside a permanent magnet. All my understanding points to magnetic force happening as a result of the movement of electrons (or any Fermion for that matter).

One cannot be selective about this sort of thing. You cannot 'see' any virtual photons and they are a very sophisticated concept - way beyond the level of this thread and yet you feel you can visualise electrons buzzing around in circles?? Physics is not a subject that takes well to the intuitive approach. Many invalid experiments and demonstrations have been used in the past. They convinced great minds at the time but have been proved wrong later. Finding something "hard to imagine" is not a good argument one way or another. At PF we. at least try to follow the protocol that's used to advance the subject.

 

[Charles Link]

Rotating the magnet has virtually no effect. The speed of the electrons, if you do a classical description, is quite high. Not at the speed of light, but perhaps 1/100 the speed of light. $\\$ Meanwhile, if you rotate the magnet on the other axis, you can get EMF's (voltages) from the Faraday effect. Suggest you read about the Faraday effect.

 

[sophiecentaur]

So I wasn't entirely wrong; there is an electric current. Its just exclusively on the very outside of the material.

If there were a current in the sense that you imply, it would be affected by the Resistance of the material and the Energy in the Permanent Field would fade. A 'permanent magnet' does not fade.

 

[sophiecentaur]

Rotating the magnet has virtually no effect. The speed of the electrons, if you do a classical description, is quite high. Not at the speed of light, but perhaps 1/100 the speed of light.

Typical electron drift speeds are around 1mm/s. Any model that's based on currents will involve some very different concept of current than conventional current.

 

[Charles Link]

Typical electron drift speeds are around 1mm/s. Any model that's based on currents will involve some very different concept of current than conventional current.

I'm referring to bound electron currents=essentially a Bohr atom approach where the electron orbits the atom. (Of course, in the case of electron spin, this model is not realistic, but the answer to the OP's manual rotation question is still the same).

 

[Charles Link]

One cannot be selective about this sort of thing. You cannot 'see' any virtual photons and they are a very sophisticated concept - way beyond the level of this thread and yet you feel you can visualise electrons buzzing around in circles?? Physics is not a subject that takes well to the intuitive approach. Many invalid experiments and demonstrations have been used in the past. They convinced great minds at the time but have been proved wrong later. Finding something "hard to imagine" is not a good argument one way or another. At PF we. at least try to follow the protocol that's used to advance the subject.

In general, most of the time when someone posts their "guesses" or what their "instincts" tell them, they have it almost all completely wrong. In this case, I think the OP actually had a couple of reasonably good guesses. I would encourage the OP @atommo to do some more reading on the subject, such as the "links" that were provided to him, but for a couple of his "guesses", he was on the right track.

 

[sophiecentaur]

; there is an electric current. Its just exclusively on the very outside of the material.

In this case the currents are essentially macroscopic effects (no?) around the outside of the material

I'm referring to bound electron currents=essentially a Bohr atom approach where the electron orbits the atom.

Here, the suggested currents are around the atom. But in a bound state round an atom, where can you say the electron 'is' to be moving in a loop?
The two ideas seem to be totally different and neither seems to be equivalent to electron spin, which is how ferromagnetism is usually explained.
I see no point in trying to bend the accepted theory to fit someones personal intuition. Where could that take @atommo further in understanding the mechanisms of magnetism if you start so far off course?

 

[Charles Link]

In this case the currents are essentially macroscopic effects (no?) around the outside of the material

Here, the suggested currents are around the atom. But in a bound state round an atom, where can you say the electron 'is' to be moving in a loop?
The two ideas seem to be totally different and neither seems to be equivalent to electron spin, which is how ferromagnetism is usually explained.
I see no point in trying to bend the accepted theory to fit someones personal intuition. Where could that take @atommo further in understanding the mechanisms of magnetism if you start so far off course?

The electron spin is different classically from orbital electron current, but in Griffiths derivation in chapter 6 of his book, he treats the case of a magnetic moment $\vec{\mu}$ of either form (spin or orbital angular momentum). (Note: $\vec{\mu}_s=\frac{g_s \mu_B \vec{S}}{\hbar}$, and $\vec{ \mu}_L=\frac{g_L \mu_B \vec{L}}{\hbar }$,(c.g.s. units), where the Bohr magneton $\mu_B=\frac{e \hbar}{2 mc}$, and where $g_s=2.0023...$ and $g_L=1.0$ ).$\\$ He considers an arbitrary distribution of such magnetic moments and derives the equation for the vector potential $\vec{A}$. This vector potential takes the form (c.g.s. units) of $\vec{A}(x)=\int \frac{\vec{J}(x')}{c|x-x'|} \, d^3x'$, where $\vec{J}$ is any arbitrary current density distribution. With a couple of vector identities, he shows that the potential from his arbitrary distribution of magnetic moments has two terms that are of the following: $\vec{A}(x)=\int \frac{\vec{M}(x') \times \hat{n}'}{|x-x'|} \, dA' +\int \frac{\nabla' \times \vec{ M}(x')}{|x-x'| } \, d^3x'$, where $\vec{M}$ is the density of magnetic moments $\vec{\mu}$ per unit volume. By looking at this result, one can conclude that the magnetic surface current density per unit length $\vec{K}_m=\vec{M} \times \hat{n}$, etc. $\\$ The first integral is the magnetic surface currents with magnetic surface current per unit length $\vec{K}_m=\vec{M} \times \hat{n}$, and the second integral involves gradients in the magnetization with bulk magnetic current density $\vec{J}_m=\nabla \times \vec{M}$, where I may have left off $\mu_o$ and/or $c$, (or a $4 \pi$ ), in a couple of places. (Switching between c.g.s. and various SI units requires a little extra work. Griffiths uses a form of SI units). $\\$ (It is left open for discussion whether these currents are real or not. There is no actual charge transport here, but these currents can be used with Biot-Savart to compute the magnetic field $\vec{B}$. Alternatively, the magnetic field is given by $\vec{B}=\nabla \times \vec{A}$ ). $\\$ Many physics students who have studied Griffiths textbook seem to overlook this very important derivation that he does. The magnetic surface currents that arise here can be used to readily explain the magnetic field of a permanent magnet of cylindrical shape that has uniform magnetization $\vec{M}$ along its axis. The magnetic surface currents can be used to compute the magnetic field that exists both inside and outside the permanent magnet.

 

[atommo]

You cannot 'see' any virtual photons and they are a very sophisticated concept - way beyond the level of this thread and yet you feel you can visualise electrons buzzing around in circles?? Physics is not a subject that takes well to the intuitive approach. Many invalid experiments and demonstrations have been used in the past. They convinced great minds at the time but have been proved wrong later. Finding something "hard to imagine" is not a good argument one way or another. At PF we. at least try to follow the protocol that's used to advance the subject.

Well not quite buzzing in circles... More like I can visualise electron clouds (since due to quantum mechanics electrons sort of appear and disappear all over a certain area rather than 'orbit' an atom). I can work out on a rather simple level the exchange of energy between these electrons. I know that electrons do not really 'spin'- its just a term used to identify the energy (virtual photon) type they give out.

I would say so long as a good base understanding is there, you can simulate quite a lot in your head (and if it gets crazy you can start writing stuff down/drawing it).

Of course you can get things wrong- science is about testing theories, getting them wrong and then getting closer to a proper understanding. And sometimes simulations don't work out either such as the case here where I needed input from others to help clear up my misunderstanding.

I'm not a maths or science guru for that matter- I do it on the side as a passion because I enjoy it (but sadly I don't know many of the formulas for that reason). But even so, that doesn't stop me from learning about for example the quanta of the electromagnetic force. I just have to try and convert the information I read into something I can understand (which may mean it is not 100% mathematically accurate, but it is usually still generally on the right lines).

Ultimately I want to make something based on what I've learned but I want to have as thorough understanding of electromagnetism as possible before that. I may be back with more crazy questions later on but for now I've got the answer I was looking for so thanks to all of you! Also in future I'm not too particular on mathematical accuracy in answers so long as it gives me a good idea because of the reason above [unless I've stated otherwise in that question] (obviously if so please say it is not completely accurate)

 

[BvU]

Oh boy ...

 

[sophiecentaur]

I want to have as thorough understanding of electromagnetism as possible before that.

Read a serious book on EM theory. There is no other way to achieve what you need.