Magnet Myths and Misconceptions

[bboj]

Quote from: TinselKoala on Today at 01:50:07 AM

You have got to get past these "why" questions, though.

See what you did there? "How" and "why" are not really the same question.
As I understand it, there are a few "free parameters"  in the modern physical description of reality. Not many, only like sixteen or something like that. Everything else takes its calculated or derived value from the seemingly arbitrary values we see of these free parameters. Nobody knows just "why" these parameters take on the values they do, but what is known is that if any of them were even slightly different, the world would be very much different. For example, let the fine structure constant be only a few percent different... and no stars can form. The situation is kind of like Euclid's Axioms. Nobody knows "why", on a perfect plane, two parallel lines never intersect. But it's easy to see _how_ that happens (or rather doesn't happen) and to use that fact to prove, with mathematical certainty, other theorems about geometry.

Sure, the explanation you seek is simple. If it were otherwise... we would not be around to see it. Eventually, when we ask "why" something in Physics is the way it is, we bump up against the Anthropic Principle, weak or strong. And as you know these explanations are less than satisfactory.

So, humans invented Religion. God did it, because He wanted it to be that way. See, it says so right here in the (insert favorite holy book here).

Ok I am asking because I want some answers from you guys with much more knowledge.
I agree with what you say about known parameters but there must exist a physical reality - now if we have a varying DC flow it has to be flow of something. Is it a flow of some primary particles or what. Could it be flow in both direction so we have an impression of a static field.
You guys have much more experience -at least some of you, I am sure you asked these questions to yourselves.
A field surely is made of something.

[TinselKoala]

Argh. Charge, motion, field: one thing. One.

What is moving? Charge. What is the smallest chunk of charge? The Unit Charge. Where are these charge chunks? The Negative one is carried by and is inseparable from the electron. The positive one is carried by the proton, and also the positron (the electron's antiparticle). Normally we never actually see those positive charge carrying particles because the proton is buried deep within the nucleus of atoms and the positron is only made in energetic reactions and doesn't stick around very long. So the positive charges we see, like on the top of a positive Van De Graaff machine, are actually "holes"... deficiencies in electrons, places where electrons should be to make everything neutral, but for some reason they aren't there.
OK, now in wires carrying current, you can think of the charge moving fast through the "electron gas" of conduction band electrons, like the momentum moves through a Newton's Balls system, or if it is easier you can think of the electrons themselves flowing along in the wire. Either way, the current (moving charge) is pushed along by the fact that at one end of the wire there is more negative charge than at the other. This of course also means that there is more _positive charge_ at the other end of the wire-- holes where electrons should be.
The reason metals don't flow and collapse from all this electron charge moving around is because there are a bloody _lot_ of electrons, a Coulomb is a huge number of them, and even with currents of kilo or megaAmperes we are still only moving a tiny fraction of the electrons in the wire.
Now, when you move a charge you get an associated magnetic field around it. The field has geometry and strength that is determined by the path and speed of the moving charge. You can think of it like the bow wave ahead of a moving boat. Each moving charge has its tiny "bow wave" of a magnetic field circling around the path of  motion. (But what acts as the "water" in this analogy? That's a very deep question.) But there are many many many charges moving in even the smallest currents. So if you were really tiny and could watch your wire, and a tiny single charge came by, being pushed from behind by MH's "field" or by charge pressure from the charges behind it (same thing) you would see a bump on your field detector as the charge came by. So a DC current--- a single moving charge -- generates a dynamic, changing field at your fixed location as the charge moves past. But there are many many many charges flowing in the tiniest real DC current, so you see what looks like a strong, static field at your measurement point, as the charges flow past so many and so fast your finest instrument can't tell them from a continuous flow of homogeneous fluid.

Now we do know why, or rather how, a boat makes a bow wave. You can't really move through the water without making one and the faster you go the bigger the wave. Charges make magnetic fields as they move relative to the observer. If the observer moves along with the charge... you don't see the magnetic field (because the field just describes how a thing will move and you are already moving that way) but you do see the electric field from the charge which isn't moving with respect to you. Now that duality of electric and magnetic fields, discriminated only by relative motion, is, to me, a grand mystery of the Universe. "Why" does that happen? Well, some people believe that that question can be answered in a meaningful way, and that's why they go out and build particle accelerators and learn complex mathematics. I just look around in awe, myself, and give thanks that things are the way they are. Maybe they could be different... but I doubt it.


eta: The electron's charge cannot be removed from it, but an electron isn't "just" a packet of the Unit Negative charge. It has mass and spin angular momentum as well. What is really weird is that it does not appear to have a "size"... it is considered a point particle, or a probability cloud.

[Newton II]

I have few interesting (crazy) questions:

1)  If you charge a van de graph generator to full extent, fix it on a truck and run the truck with 100km/hr speed will the generator sphere
     create a 'mega magnetic field'?  Because moving charges should create magnetic field.   If not 'Why'?

2)  Negative and positive charges are characteristically  opposite charges. So, when a moving negative charge produces magnetic field, a
     moving positive charge should produce anti-magnetic field.  But it just produces a magnetic field in opposite direction corresponding to
     the negative charge flow. 'Why'?   

3)  When moving charges (current) produces a magnetic field, reversely a moving magnetic field should produce an electric current. That is
     the principle used in an Electric generator.  But all generators are AC generators (alternators)  in which the current is first generated
     only in AC form  and later converted to DC by using split ring commutator.   A moving magnetic field cannot straightaway produce a
     DC.   'Why?'     

Can any genious answer?

[Liberty]

Argh. Charge, motion, field: one thing. One.

What is moving? Charge. What is the smallest chunk of charge? The Unit Charge. Where are these charge chunks? The Negative one is carried by and is inseparable from the electron. The positive one is carried by the proton, and also the positron (the electron's antiparticle). Normally we never actually see those positive charge carrying particles because the proton is buried deep within the nucleus of atoms and the positron is only made in energetic reactions and doesn't stick around very long. So the positive charges we see, like on the top of a positive Van De Graaff machine, are actually "holes"... deficiencies in electrons, places where electrons should be to make everything neutral, but for some reason they aren't there.
OK, now in wires carrying current, you can think of the charge moving fast through the "electron gas" of conduction band electrons, like the momentum moves through a Newton's Balls system, or if it is easier you can think of the electrons themselves flowing along in the wire. Either way, the current (moving charge) is pushed along by the fact that at one end of the wire there is more negative charge than at the other. This of course also means that there is more _positive charge_ at the other end of the wire-- holes where electrons should be.
The reason metals don't flow and collapse from all this electron charge moving around is because there are a bloody _lot_ of electrons, a Coulomb is a huge number of them, and even with currents of kilo or megaAmperes we are still only moving a tiny fraction of the electrons in the wire.
Now, when you move a charge you get an associated magnetic field around it. The field has geometry and strength that is determined by the path and speed of the moving charge. You can think of it like the bow wave ahead of a moving boat. Each moving charge has its tiny "bow wave" of a magnetic field circling around the path of  motion. (But what acts as the "water" in this analogy? That's a very deep question.) But there are many many many charges moving in even the smallest currents. So if you were really tiny and could watch your wire, and a tiny single charge came by, being pushed from behind by MH's "field" or by charge pressure from the charges behind it (same thing) you would see a bump on your field detector as the charge came by. So a DC current--- a single moving charge -- generates a dynamic, changing field at your fixed location as the charge moves past. But there are many many many charges flowing in the tiniest real DC current, so you see what looks like a strong, static field at your measurement point, as the charges flow past so many and so fast your finest instrument can't tell them from a continuous flow of homogeneous fluid.

Now we do know why, or rather how, a boat makes a bow wave. You can't really move through the water without making one and the faster you go the bigger the wave. Charges make magnetic fields as they move relative to the observer. If the observer moves along with the charge... you don't see the magnetic field (because the field just describes how a thing will move and you are already moving that way) but you do see the electric field from the charge which isn't moving with respect to you. Now that duality of electric and magnetic fields, discriminated only by relative motion, is, to me, a grand mystery of the Universe. "Why" does that happen? Well, some people believe that that question can be answered in a meaningful way, and that's why they go out and build particle accelerators and learn complex mathematics. I just look around in awe, myself, and give thanks that things are the way they are. Maybe they could be different... but I doubt it.


eta: The electron's charge cannot be removed from it, but an electron isn't "just" a packet of the Unit Negative charge. It has mass and spin angular momentum as well. What is really weird is that it does not appear to have a "size"... it is considered a point particle, or a probability cloud.

Wonderful evidence of an intelligent designer (creator) that perfectly formed what we are just beginning to understand, just how He designed things to work in the universe.  We have the opportunity to personally come to understand and know what that intelligent engineer (creator) of perfection knows, and what he can further reveal to us and teach us about His universe and ourselves?  A close relationship with the great engineer of the universe: (Jesus Christ) that engineered the functioning of the electron, the magnetic fields, and the entire atomic world and universe.  To gain more knowledge and understanding from the original source of all knowledge and wisdom and power.  The Alpha and Omega.  (The beginning and the end).

[poynt99]

Quote from: TinselKoala on Today at 01:50:07 AM

You have got to get past these "why" questions, though.

See what you did there? "How" and "why" are not really the same question.

I agree, and I made reference to that in a previous post.

However bboj was making reference to my question, which was "how", even though he used "why". So I suspect that is what he meant.

Anyway, thanks for the explanation, I do agree, based on the reading I have been doing. So, my simple explanation is as follows:

When a DC voltage is applied across a wire, the free conduction electrons are repelled from the negative electrode towards the positive electrode. The free electrons do not and can not move instantly from one end to the other due to scattering and collisions with other electrons. Each electron carries charge, and moving charge induces a moving magnetic field. But since the electrons do not instantly bolt from one end to the other, rather than a microscopic movement of charge, there is a macroscopic movement of charge from one end to the other. This macroscopic movement of charge is near the speed of light and results in a macroscopic magnetic field that we can measure around the wire.

A charge has an electric field, and it is the movement of the E field that produces the B field. The macroscopic moving E field in the wire is very much like the "moving" B field of a Faraday disc; i.e. even though the electrons producing the field are moving, the resulting produced field appears to be static. That's why a DC current in a wire does not induce a current in an adjacent open circuit wire. The field is not changing, relative to the other stationary wire. Yep special relativity comes into play and is responsible for mag fileds around wires and also the electromagnet.

When an AC source is applied to the same wire, we have the same scenario where the B field is produced, but in this case the field is not only alternating directions, but it is changing, i.e. varying in magnitude. It is this varying field that can induce a current in an adjacent wire. Induction is another related topic for another discussion perhaps.