Curious device

[exchemist]

24 minutes ago, Mordred said:

The E field not the B field. Doesn't matter if it's a permanent magnet or an electromagnet it's still the same.

To help understand the permanent magnet if you look at inductance it does have both the E and B fields .

The reason why the B field has less energy and doesn't do the work involves how the field diverges as opposed to the E field coupled with the Lorentz force law via the right hand rule. That directly relates to Swnsonts previous statement with regards to the cross product for the B field as opposed to the inner product of the E field

OK, but what gives rise to the E field in this case and what form does it take?

 

[Mordred]

21 minutes ago, exchemist said:

OK, but what gives rise to the E field in this case and what form does it take?

 

The better question is what gives rise to the B field. The E field current generates the B field. With permanent magnets the E field current is generated due to the electron charge alignments as per ferromagnetism so there is always an E field current allowing the B field

If you take a rotor for example and law it on its side so the opening is facing you the E field current will be through the center of the rotor heading either towards you or away from you depending on the magnetic pole alignment. What allows the rotor to turn depends on varying the E currents with the different poles of the rotor. Typically 3 poles for 3 phase motors. The phase shifts provides the differences in current in each pole. It is still the E field performing the work.

For DC motors it's much the same you send pulses at selected poles to generate the field variations to induce rotation. The number of poles is equal to the number of signal wires the device has and you send pulse patterns to the DC stepper motor.

Edited April 21 by Mordred

[sethoflagos]

6 hours ago, exchemist said:

If a nail is attracted towards a permanent magnet, doing work against friction, where does the energy come from?

I suspect that the guarded responses you've received to this query so far are because the simple answer we used to be given at school was bowlocks and sort of implied the existence of magnetic monopoles. Hence no self-respecting physicist will go down that path.

As I don't fall into the above category, I'm quite content to picture the energy source as a form of potential energy created by the separation between the nail and the magnet. Much akin to gravitational or (ahem) Coulomb potential.

As nail approaches magnet, potential energy begets kinetic energy begets heat (in collision) producing a new magnet that is the sum of its initial magnetic dipole moments, just as a meteor descending to earth creates a new body that is the sum of their individual masses.

Now I am expecting this simplistic picture to be shot down in flames, but then I too will be wondering (in the absence of electrical current) where the energy came from.

 

[Mordred]

1 hour ago, sethoflagos said:

I suspect that the guarded responses you've received to this query so far are because the simple answer we used to be given at school was bowlocks and sort of implied the existence of magnetic monopoles. Hence no self-respecting physicist will go down that path.

As I don't fall into the above category, I'm quite content to picture the energy source as a form of potential energy created by the separation between the nail and the magnet. Much akin to gravitational or (ahem) Coulomb potential.

As nail approaches magnet, potential energy begets kinetic energy begets heat (in collision) producing a new magnet that is the sum of its initial magnetic dipole moments, just as a meteor descending to earth creates a new body that is the sum of their individual masses.

Now I am expecting this simplistic picture to be shot down in flames, but then I too will be wondering (in the absence of electrical current) where the energy came from.

 

It might help to consider even in atoms electrons never stay still. In permanent magnets those electrons are moving around within the atoms of the magnet as well as the environment. However magnetism isn't a force nor is it a form of energy. A common analogy is to think of it as a translator with the E field. It results from the E field current and can thus be used to affect the E field through induction.

lol you also run into articles etc stating permanant magnets have no E field but that wouldn't be true. The atoms have electrons and is held together by the EM field. So when you move the magnet to the nail your really just inducing electric current in a field already present which does the work via electromagnetic induction. (keep in mind I'm keeping the mediator photons out of the equation for this discussion) ie keeping it classical rather than quantum lol

Edited April 21 by Mordred

[sethoflagos]

2 hours ago, Mordred said:

However magnetism isn't a force nor is it a form of energy. A common analogy is to think of it as a translator with the E field. It results from the E field current and can thus be used to affect the E field through induction.

This reminds me of how pressure is not an 'energy' but mediates the transfer of internal energy of a gas which is a function of temperature alone. However, pressure is a 'force' so that analogy breaks down.

I did wonder why electron charge cropped up as a coefficient on both terms of the Lorentz force, both the E and vxB terms. So without q there is no electromagnetic force. Is this what you mean? That the B field is merely a mechanism for transforming dynamic changes to the Coulomb force into a torsional effect?  

[swansont]

10 minutes ago, sethoflagos said:

However, pressure is a 'force' so that analogy breaks down.

It’s more than whether it’s a force. Work requires a force acting through a displacement. A centripetal force, for example, does no work because force and displacement are perpendicular. Pressure is not an energy, but pressure can do work.

[Mordred]

I like your example +1

in point of detail Amperes law teaches us that all magnetic phenomena is the result of electric charges in motion. Faraday discovered moving magnets generates  an electric current. Maxwell and Lorentz in essence put together the final touch that E and B are not separate entities but are inexplicitly intertwined. So even a point charge has  E and B fields. Now it takes a charge to produce an electromagnetic field, but just as importantly is that it takes another charge to detect an electromagnetic field.

Now when you have an ensemble of charges you use the principle of superposition which tells us the interaction of two charges is unaffected by the presence of others. So you can compute the force resulting from each charge to the test charge and sum up to the total vector sum for total force on the test charge. Now you probably recognize I just described the electrostatic field. However with that field you now have to think in terms of charge density and charge currents. (By the way this applies to QFT as well) including the Feymann path integrals, just an FYI). So in point of detail the force on the test charge results from the sum of force of the individual point charges mediated by the EM field. 

Now we can further break down this Electrostatic field into  surface charge, line charge, continuous distribution and volume charge. Each has has its own integral combined with Coulombs law.

for example

charge distribution \[E_r=\frac{1}{4\pi \epsilon_0}\int\frac{1}{r^2}\hat{r}dq\]

line distribution  \[E_r=\frac{1}{4 \pi\epsilon_0}\int \frac{\lambda(\acute{r})}{r^2}\hat{r}d\acute{l}\]

surface charge 

\[E_r=\frac{1}{4 \pi\epsilon_0}\int\frac{\sigma(\acute{r})}{r^2}\hat{r}d \acute{a}\] and volume charge which we use most often. as being the one most referred to with Coulombs law

\[E_r=\frac{1}{4 \pi\epsilon_0}\int\frac{\rho(\acute{r})}{r^2}\hat{r}d\acute{\tau}\]

So knowing that according to Amperes law magnetism is the result of electric charges in motion. One has to ask well how does a permanent magnet work. What materials  are more likely to make a magnet which materials would make a stronger magnet? To better understand that one has to understand how readily a material accepts domain realignment via a process called hysteresis.  However it should be more clear that the charge distributions described by the formulas above directly relates to the sum of coulomb force to the test charge "d" is domain while the identifier after it is the domain type. the "r" with the hat is the distance from the domain to the test charge.

So ferromagnets has domains with domain walls the walls are potential difference separations each domain has its own hysteresis. Histeresis describes a phenomena that when you pass a magnet near a ferrous material the alignments of the point charges do not return to the original configuration. (ever have a screw driver that you often use to work on an electric circuit eventually become a permanent magnet ? ) its due to hysteresis.

hope that helps better understand the electrostatic field and ferromagnetism

So now you should be able to answer the question :" Where does the energy come from" in the permanent magnet case...think domain charge densities and hysteresis due to the magnet interacting with the nail. This will also help when you look at things like Currie temperature and how it effectively it can be used to realign domains

The domain alignments has potential energy there is no outside interaction so no current flow but you still have a charge density. When you place the nail near the magnet to interact the interaction exchange results in a charge current flow. This describes a kinetic energy term mediating the force.

Now unfortunately a lot textbooks teach flow of electrons in a copper wire etc. It isn't the flow of electrons, its the flow of charge. Electrons could not flow through a medium fast enough for one thing. However the flow of charge can as charge is mediated by photons. It serves as the momentum carrier to alter the spin alignments of the electron ensemble

edit forgot to add the primes (I tend to use acute ) are the source coordinates of the given domain for example \(d \acute{a}\). The symbols \(\lambda, \sigma,  \rho\) is charge per unit (length, area, volume). 

The above also helps better understand induction. Your inducing charge current.

Edited April 22 by Mordred

[Prajna]

4 hours ago, Mordred said:

I like your example +1

in point of detail Amperes law teaches us that all magnetic phenomena is the result of electric charges in motion. Faraday discovered moving magnets generates  an electric current. Maxwell and Lorentz in essence put together the final touch that E and B are not separate entities but are inexplicitly intertwined. So even a point charge has  E and B fields. Now it takes a charge to produce an electromagnetic field, but just as importantly is that it takes another charge to detect an electromagnetic field.

Now when you have an ensemble of charges you use the principle of superposition which tells us the interaction of two charges is unaffected by the presence of others. So you can compute the force resulting from each charge to the test charge and sum up to the total vector sum for total force on the test charge. Now you probably recognize I just described the electrostatic field. However with that field you now have to think in terms of charge density and charge currents. (By the way this applies to QFT as well) including the Feymann path integrals, just an FYI). So in point of detail the force on the test charge results from the sum of force of the individual point charges mediated by the EM field. 

Now we can further break down this Electrostatic field into  surface charge, line charge, continuous distribution and volume charge. Each has has its own integral combined with Coulombs law.

for example

charge distribution

Er=14πϵ0∫1r2r^dq

 

line distribution 

Er=14πϵ0∫λ(r´)r2r^dl´

 

surface charge 

 

Er=14πϵ0∫σ(r´)r2r^da´

and volume charge which we use most often. as being the one most referred to with Coulombs law

 

 

Er=14πϵ0∫ρ(r´)r2r^dτ´

 

So knowing that according to Amperes law magnetism is the result of electric charges in motion. One has to ask well how does a permanent magnet work. What materials  are more likely to make a magnet which materials would make a stronger magnet? To better understand that one has to understand how readily a material accepts domain realignment via a process called hysteresis.  However it should be more clear that the charge distributions described by the formulas above directly relates to the sum of coulomb force to the test charge "d" is domain while the identifier after it is the domain type. the "r" with the hat is the distance from the domain to the test charge.

So ferromagnets has domains with domain walls the walls are potential difference separations each domain has its own hysteresis. Histeresis describes a phenomena that when you pass a magnet near a ferrous material the alignments of the point charges do not return to the original configuration. (ever have a screw driver that you often use to work on an electric circuit eventually become a permanent magnet ? ) its due to hysteresis.

hope that helps better understand the electrostatic field and ferromagnetism

So now you should be able to answer the question :" Where does the energy come from" in the permanent magnet case...think domain charge densities and hysteresis due to the magnet interacting with the nail. This will also help when you look at things like Currie temperature and how it effectively it can be used to realign domains

The domain alignments has potential energy there is no outside interaction so no current flow but you still have a charge density. When you place the nail near the magnet to interact the interaction exchange results in a charge current flow. This describes a kinetic energy term mediating the force.

Now unfortunately a lot textbooks teach flow of electrons in a copper wire etc. It isn't the flow of electrons, its the flow of charge. Electrons could not flow through a medium fast enough for one thing. However the flow of charge can as charge is mediated by photons. It serves as the momentum carrier to alter the spin alignments of the electron ensemble

edit forgot to add the primes (I tend to use acute ) are the source coordinates of the given domain for example da´ . The symbols λ,σ,ρ is charge per unit (length, area, volume). 

The above also helps better understand induction. Your inducing charge current.

Splendid. Now all I need is for someone like @exchemist to translate this into simple terms that I can comprehend. I am still studying the wiki, btw, in the hope that I can get to a broad-brush understanding of how magnetism works.

[exchemist]

16 hours ago, Mordred said:

The better question is what gives rise to the B field. The E field current generates the B field. With permanent magnets the E field current is generated due to the electron charge alignments as per ferromagnetism so there is always an E field current allowing the B field

If you take a rotor for example and law it on its side so the opening is facing you the E field current will be through the center of the rotor heading either towards you or away from you depending on the magnetic pole alignment. What allows the rotor to turn depends on varying the E currents with the different poles of the rotor. Typically 3 poles for 3 phase motors. The phase shifts provides the differences in current in each pole. It is still the E field performing the work.

For DC motors it's much the same you send pulses at selected poles to generate the field variations to induce rotation. The number of poles is equal to the number of signal wires the device has and you send pulse patterns to the DC stepper motor.

OK, I'm trying to follow this in the context of a permanent magnet. I'm not finding the motor analogy very helpful (sorry, my background is chemistry rather than engineering). I'm aware that ferromagnetism arises due to aligned, unpaired electron intrinsic "spin" and orbital angular momentum. So I presume the "current" you refer to in this case would comprise the "spinning" (not really but let's call it that) and orbital motion of the electrons. Is that right? But it seems to me this aligned angular momentum does not lead to an overall E field external to a bar magnet, which can interact with a nail some distance away. Or does it?

If, as you say, the energy in the magnet that changes, when the nail is brought close to it, comes from the E field, what change do we get at the atomic level? Are we saying the quantum states of the unpaired electrons drop slightly in electrostatic energy, e.g. their mean distance from the nucleus reduces fractionally, or something like that?    

21 minutes ago, Prajna said:

Splendid. Now all I need is for someone like @exchemist to translate this into simple terms that I can comprehend. I am still studying the wiki, btw, in the hope that I can get to a broad-brush understanding of how magnetism works.

As you will see, I am trying to get a physics tutorial on this from @Mordred, who is I gather a professional physicist (respect).

It looks to me so far (i.e. pending what I may be about to learn) that I may have been a bit too cavalier in strict physics terms in claiming the work done by, and on,  your magnets comes from what I have been calling "the magnetic field". We are now into a discussion of the E field and the B field and where exactly the extra energy due to magnetisation resides in a permanent magnet.

I think though that, in terms intelligible to a non-physicist, we can still say it is the extra energy in the fields due to their magnetised condition that rises and falls as work is done.  

But let's see what brother Mordred comes back with. I just hope I have enough grey cells left, at approaching 70, to take in a change in my mental picture of how this all works. 😀

Edited April 22 by exchemist

[Prajna]

2 hours ago, exchemist said:

OK, I'm trying to follow this in the context of a permanent magnet. I'm not finding the motor analogy very helpful (sorry, my background is chemistry rather than engineering). I'm aware that ferromagnetism arises due to aligned, unpaired electron intrinsic "spin" and orbital angular momentum. So I presume the "current" you refer to in this case would comprise the "spinning" (not really but let's call it that) and orbital motion of the electrons. Is that right? But it seems to me this aligned angular momentum does not lead to an overall E field external to a bar magnet, which can interact with a nail some distance away. Or does it?

If, as you say, the energy in the magnet that changes, when the nail is brought close to it, comes from the E field, what change do we get at the atomic level? Are we saying the quantum states of the unpaired electrons drop slightly in electrostatic energy, e.g. their mean distance from the nucleus reduces fractionally, or something like that?    

As you will see, I am trying to get a physics tutorial on this from @Mordred, who is I gather a professional physicist (respect).

It looks to me so far (i.e. pending what I may be about to learn) that I may have been a bit too cavalier in strict physics terms in claiming the work done by, and on,  your magnets comes from what I have been calling "the magnetic field". We are now into a discussion of the E field and the B field and where exactly the extra energy due to magnetisation resides in a permanent magnet.

I think though that, in terms intelligible to a non-physicist, we can still say it is the extra energy in the fields due to their magnetised condition that rises and falls as work is done.  

But let's see what brother Mordred comes back with. I just hope I have enough grey cells left, at approaching 70, to take in a change in my mental picture of how this all works. 😀

Watching from the sidelines with avid interest...

[Eise]

Just a tiny remark. As Swansont already said, it is like a chain. Now just 'zoom in into' these chain: it is all EM fields. But you do not ask how all these do work. But the macroscopic magnetic field is not different in this respect. It is just the intermediate of the force, but does no work itself.

[Mordred]

2 hours ago, exchemist said:

OK, I'm trying to follow this in the context of a permanent magnet. I'm not finding the motor analogy very helpful (sorry, my background is chemistry rather than engineering). I'm aware that ferromagnetism arises due to aligned, unpaired electron intrinsic "spin" and orbital angular momentum. So I presume the "current" you refer to in this case would comprise the "spinning" (not really but let's call it that) and orbital motion of the electrons. Is that right? But it seems to me this aligned angular momentum does not lead to an overall E field external to a bar magnet, which can interact with a nail some distance away. Or does it?

If, as you say, the energy in the magnet that changes, when the nail is brought close to it, comes from the E field, what change do we get at the atomic level? Are we saying the quantum states of the unpaired electrons drop slightly in electrostatic energy, e.g. their mean distance from the nucleus reduces fractionally, or something like that?    . 

Your fairly close to the right idea. Without going into the quantum regime too intensely. In essence the overall electron spin up/ spin down alignments contained in each domain gets altered.  Some electrons will switch from spin up to spin down or the overall orientation changes by some angle. 

So the fields of the magnet is already present even when it's not interacting with another object. So the charge currents are essentially zero (it's never truly zero as there is always some electron exchanges). So one can equate this to the PE term (potential energy)

When the nail interacts with the magnet. The interaction of the magnet including the B field provide directivity of the charge current that results from the interaction between the magnet and the nail. We see this directivity in the magnetic field lines. The tighter the field lines the greater the amount of force. So further away the field lines diverge and gets weaker. (1/r^2).

So in essence the electrostatic field does the work. The B field interaction in essence provides directivity of the charge current. A charge current is a kinetic energy term. 

 

 

[Prajna]

11 minutes ago, Mordred said:

So in essence the electrostatic field does the work. The B field interaction in essence provides directivity of the charge current. A charge current is a kinetic energy term. 

And from this is where we get the idea that the magnet is redirecting force rather than doing work? Ah ok, it starts to make sense. And really I should be thinking in terms of induced electrostatic forces rather than magnetic forces? Am I getting closer?

[Mordred]

15 minutes ago, Prajna said:

And from this is where we get the idea that the magnet is redirecting force rather than doing work? Ah ok, it starts to make sense. And really I should be thinking in terms of induced electrostatic forces rather than magnetic forces? Am I getting closer?

Excellent precisely what you should be of it in terms of

[Prajna]

The device is now available on GitHub, for anyone who would like to build and experiment with it. Hopefully today I will get to FabLab to see about printing and assembling one to test.

Git is at: https://github.com/prajna-pranab/SFT

 

[exchemist]

2 hours ago, Prajna said:

The device is now available on GitHub, for anyone who would like to build and experiment with it. Hopefully today I will get to FabLab to see about printing and assembling one to test.

Git is at: https://github.com/prajna-pranab/SFT

 

How do you print a permanent magnet?

[Prajna]

15 minutes ago, exchemist said:

How do you print a permanent magnet?

Hmm, maybe you can do it with iron nitride magnets. They can be manufactured and then magnetised in place. You'd need an expensive printer to print the shafts, axles and fingers too (I'm planning to get them laser cut).

[exchemist]

38 minutes ago, Prajna said:

Hmm, maybe you can do it with iron nitride magnets. They can be manufactured and then magnetised in place. You'd need an expensive printer to print the shafts, axles and fingers too (I'm planning to get them laser cut).

Expect you can buy neodymium alloy magnets on the internet these days. Make sure you don't trap your fingers. They can be a safety hazard.  

[Eise]

31 minutes ago, exchemist said:

Expect you can buy neodymium alloy magnets on the internet these days. Make sure you don't trap your fingers. They can be a safety hazard.  

... yep. And make sure you don't let them clash together. Either they will break, because they are very brittle, or you have to remove them sideways with pincers. And I imagine assembling them into a bigger contraption might be very difficult, due to their magnetic strength.

I only know this address in Switzerland, ordered a few of them:

https://www.supermagnete.ch/

 

[Prajna]

29 minutes ago, Eise said:

... yep. And make sure you don't let them clash together. Either they will break, because they are very brittle, or you have to remove them sideways with pincers. And I imagine assembling them into a bigger contraption might be very difficult, due to their magnetic strength.

I only know this address in Switzerland, ordered a few of them:

https://www.supermagnete.ch/

 

I have some 10mm X 2mm, I think N52, suitable for this device.

[Prajna]

A little update: yesterday I went to visit my local FabLab to dicuss getting some support from them. The guy took one look at the model and said, "Oh yeah, we can print that easy," which is rather reassuring, since I've never 3D printed anything and this is the first time I've designed for 3D printing. The FabLab have an event all this week, so are a bit busy, but I have emailed the lab manager and hope to get an appointment to go and discuss the project early next week. Meanwhile, in case anyone fancies getting in ahead, the full project is hosted on my GitHub (referenced above) so you can download and experiment. There are still a few issues with render materials that I am working on with the Render Workbench developer but otherwise the model should be pretty much ready to work with.