Thread: Magnetic field vs. Magnetic force?

As I work through trying to understand magnetism, I kind of get confused by the two things. Let me see if I understand this right:

A magnetic field magnetizes an object. For example, a piece of iron when placed inside a magnetic field begins to attract other pieces of iron.

A magnetic force exists between magnetized objects, like a compass needle and the north pole.


Magnetic fields can't move things on their own, right? Magnetized objects push and pull off of each other, but all the magnetic field does is decide what state of magnetism an object will experience? A single piece of metal, placed in a magnetic field, would not begin moving until another object enters the area for it to act on/be acted on?

Originally Posted by kojax

As I work through trying to understand magnetism, I kind of get confused by the two things. Let me see if I understand this right:

A magnetic field magnetizes an object. For example, a piece of iron when placed inside a magnetic field begins to attract other pieces of iron.

A magnetic force exists between magnetized objects, like a compass needle and the north pole.


Magnetic fields can't move things on their own, right? Magnetized objects push and pull off of each other, but all the magnetic field does is decide what state of magnetism an object will experience? A single piece of metal, placed in a magnetic field, would not begin moving until another object enters the area for it to act on/be acted on?

Nope.

Homogenous magnetic field is good for magnetizing.

The opposite kind of magnetic field is good for pulling and pushing.

I don't remember the word. Unhomogenous?

Inhomogenous* possible stretch to asymmetric... :-D

A magnetic field is a field produced by a magnetic object or particle (or by a changing electrical field - Faraday stuff)

A magnetic force is caused by the magnetic field, and is proportional to that field strength.

Force, measured in Newtons (shorthand 'F'), magnetic field, measured in Telsa. (shorthand 'B')

When piece of iron is being magnetized by an inhomogenous magnetic field then
first it becomes magnetic, then it starts to move.

When piece of iron is being magnetized by a homogenous magnetic field then
first it becomes magnetic, then it stays still ....... then maybe an inhomogenous
magnetic field might arrive and start moving the piece of iron that the homogenous
magnetic field had magnetized.

It's safe to disregard everything that jartsa posts as irrelevant and wrong.

Originally Posted by kojax

As I work through trying to understand magnetism, I kind of get confused by the two things. Let me see if I understand this right:

A magnetic field magnetizes an object. For example, a piece of iron when placed inside a magnetic field begins to attract other pieces of iron.

A magnetic force exists between magnetized objects, like a compass needle and the north pole.


Magnetic fields can't move things on their own, right? Magnetized objects push and pull off of each other, but all the magnetic field does is decide what state of magnetism an object will experience? A single piece of metal, placed in a magnetic field, would not begin moving until another object enters the area for it to act on/be acted on?

Neither the magnetic nor the electric field are "force" fields. Forces result from the electric and magnetic fields, according to the Lorentz force law



http://en.wikipedia.org/wiki/Lorentz_force

The force that is felt between magnets is due to the magnetic moment and is quite a bit more complicated to describe.

http://en.wikipedia.org/wiki/Magnetic_moment

You can safely ignore jartsa. As usual, he doesn't know what he is talking about. [/tex]

Just to clarify Dr.Rocket on a typo:

The lorentz force is:

Magnetic field is the field where any magnetic material can be affected inside.

Originally Posted by onurtuna

Magnetic field is the field where any magnetic material can be affected inside.

Nope.

In fact your sentence makes no sense.

When a charge moves, it can affect the moving charges. There is no field but the moving charge can affect another moving charge through an area and there are bounds. We say that this area is a field and if you put a magnetic material inside this field, it will be affected. There is no real field. But we represent it with a limited field.

My sentence above is a bit more basic and it makes sense so.

Originally Posted by onurtuna

When a charge moves, it can affect the moving charges. There is no field but the moving charge can affect another moving charge through an area and there are bounds. We say that this area is a field and if you put a magnetic material inside this field, it will be affected. There is no real field. But we represent it with a limited field.

My sentence above is a bit more basic and it makes sense so.

Neither of your posts make sense.

You don't know anything about Calculus and Electromagnetic Theory.

You don't know anything about writing clearly in English. Dr. Rocket most certainly knows about calculus and electromagnetic theory. You may do, but your ability to communicate it is currently close to zero.

But he must be kind. He doesn't know to communicate, even he knows English.

It would be delightful if he were kind, but its not in his nature. He is not being cruel, just very direct. Old farts get that way.

You are not kind also. Just discuss about Physics here.

Ok. Let me get this straight then. The only force present in a situation involving magnetism and electricity is the Lorentz force, right? And it follows this very interesting right hand rule, where it always pushes/pulls in a direction perpendicular to both the electric and magnetic fields.



(The image is taken from: http://en.wikipedia.org/wiki/Lorentz_force I is the electric field. B is the magnetic field. F is the force.)


Working off of that, I think I can only begin to try and understand how it is exactly that a permanent magnet is able to exert a force on a metal.

Originally Posted by onurtuna

You are not kind also. Just discuss about Physics here.

onortuna, are you familiar with the Enlish phrase "Get real"? It means please stop living in an imaginary world and pretending things are the way you want them, not the way they are.

You are the one who introduced personal matters into this by claiming that Dr. Rocket, who is very well versed in mathematics and physics, knew nothing about either subject. If you intend to make attacks on the knowledge level of established forum members than you must expect to receive comments in response.

Dr. Rockets comments were correct. Your posts did not make sense. Dr. Rocket could have been kind and made allowances for the fact that English is not your native language. That would be the polite thing to do. But as you just pointed out this is a forum for discussing physics and he did that objectively. Your posts made no sense. He said so.

I hope you will continue to post and I hope some other members with more patience and a knowledge of physics will make an effort to understand what you were trying to say and discuss it further with you. In the meantime I advise you not to be so sensitive to what others may say on this or any other forum.

Have a nice day.

Originally Posted by kojax

Ok. Let me get this straight then. The only force present in a situation involving magnetism and electricity is the Lorentz force, right? And it follows this very interesting right hand rule, where it always pushes/pulls in a direction perpendicular to both the electric and magnetic fields.



(The image is taken from: http://en.wikipedia.org/wiki/Lorentz_force I is the electric field. B is the magnetic field. F is the force.)


Working off of that, I think I can only begin to try and understand how it is exactly that a permanent magnet is able to exert a force on a metal.

The Lorentz force describes the force on a moving electric charge in the presence of a magnetic field. If you are interested in the force exerted on a magnetic material in a magnetic field then you need to consider the magnetic moment, as noted earlier. It is rather difficult to describe that directly in terms of the Lorentz force.

Originally Posted by onurtuna

You don't know anything about Calculus and Electromagnetic Theory.

Sonny, on the contraty I know quite a bit about both of those subjects.

Well, this is quite simple.

Green arrow means electric current.

The green wire is attracted to some electric current up there where the red arrow points.

Compass points to blue arrows direction, but that's not important.

Now the thing I'm wondering is: wouldn't an electromagnetic wave constantly experience a Lorentz force? Or does the force not apply because it doesn't contain a moving electric charge?

But, if there were a moving charge located at the center of a beam of electromagnetic radiation, would it experience the Lorentz force? Is this what causes electrons to move to higher orbitals?

Originally Posted by jartsa

Well, this is quite simple.

Green arrow means electric current.

The green wire is attracted to some electric current up there where the red arrow points.

Compass points to blue arrows direction, but that's not important.

That's not exactly how it works. The only electrical current present is that flowing through the green wire. The green wire will be compelled to move in the red direction even if there were nothing up there but empty space. Rail guns work on this principle.


This might help:

http://science.howstuffworks.com/rail-gun1.htm

[/quote]



Well, this is quite odd.

Where is the opposite direction current that repulses the current in the armature?

Must be some relativistic direction transformation thing going on here.

Originally Posted by jartsa

Well, this is quite odd.

Where is the opposite direction current that repulses the current in the armature?

Must be some relativistic direction transformation thing going on here.[/quote]Nope. It's quite simply an electric circuit of intensely high current and voltage, that creates a very massive EMF. On current, one circuit. You still have no idea what you are talking about, ever.

Originally Posted by kojax

Now the thing I'm wondering is: wouldn't an electromagnetic wave constantly experience a Lorentz force? Or does the force not apply because it doesn't contain a moving electric charge?

But, if there were a moving charge located at the center of a beam of electromagnetic radiation, would it experience the Lorentz force? Is this what causes electrons to move to higher orbitals?

An electromanetic wave is a bunch of photons and photons do not feel the electromagnetic force, so no an electromagnetic wave does not experience the Lorentz force.

A moving charge does experience the electromagnetic force, as represented by the Lorentz force equation. That has nothing to do with whether or not it is in the "center" of an a beam of electromagnetic radiation. It only requires a charged particle and an electromagnetic field.

The movement of electrons among orbitals is a subject that is governed by quantum mechanics, the best formulation of which is quantum electrodynamics, but this is something apart from the Lorentz force equation of classical electrodynamics.

Originally Posted by DrRocket

A moving charge does experience the electromagnetic force, as represented by the Lorentz force equation. That has nothing to do with whether or not it is in the "center" of an a beam of electromagnetic radiation. It only requires a charged particle and an electromagnetic field.

So, could a radio wave cause a charged particle to move? It meets the condition of having an electric and magnetic field at right angles to each other, but it seems like it would violate Newton's 3rd law. What is the charged particle exerting a force back on?

Originally Posted by Arcane_Mathematician

Nope. It's quite simply an electric circuit of intensely high current and voltage, that creates a very massive EMF. On current, one circuit. You still have no idea what you are talking about, ever.

Well, Einstein's theory of magnetism says the current in rail 1 repels current in rail 2.

Maybe it would be better to say electrons in different frames repel with increased force.

Probably also electrons in armature repel electrons in rails with extra force.

This seems to be quite simple again.

Originally Posted by kojax

Originally Posted by DrRocket

A moving charge does experience the electromagnetic force, as represented by the Lorentz force equation. That has nothing to do with whether or not it is in the "center" of an a beam of electromagnetic radiation. It only requires a charged particle and an electromagnetic field.

So, could a radio wave cause a charged particle to move? It meets the condition of having an electric and magnetic field at right angles to each other, but it seems like it would violate Newton's 3rd law. What is the charged particle exerting a force back on?

Yes an electromagnetic wave can cause a charged particle to move.

When a charged particle accelerates it also radiates an electromagnetic wave.

One has to be quite careful with Newton's third law and electromagnetic forces. They do not obey the part about the forces being directed along opposite vectors connecting the points in question (equal, opposite and colinear) -- see for instance the cautions in Goldstein's Classical Mechanics. Also note that time-varying electromagnetic fields are not conservative (generators would work if they were).

You made a good observation and points out that Newton's laws, while they apply in ordinary mechanics need to be considered much more closely when electromagnetic fields are at work. In reality, Maxwell's equations are more fundamental than are Newton's, and that is reflected in the fact that Maxwell's equations are consistent with special relativity, while Newton's are, quite clearly, not.

Note also that in Newtonian theory forces are exerted instantaneously, while in electromagnetic theory fields propagate at a finite speed. This again is reflected in compatibility or lack thereof with special relativity.

Originally Posted by DrRocket

Originally Posted by kojax

Originally Posted by DrRocket

A moving charge does experience the electromagnetic force, as represented by the Lorentz force equation. That has nothing to do with whether or not it is in the "center" of an a beam of electromagnetic radiation. It only requires a charged particle and an electromagnetic field.

So, could a radio wave cause a charged particle to move? It meets the condition of having an electric and magnetic field at right angles to each other, but it seems like it would violate Newton's 3rd law. What is the charged particle exerting a force back on?

Yes an electromagnetic wave can cause a charged particle to move.

When a charged particle accelerates it also radiates an electromagnetic wave.

So, do positive and negative particles get pushed in the same direction or in opposite directions by the Lorentz force? Most matter is composed both of protons and electrons, so I'm trying to understand why neutrally charged objects don't move. Is it because the positive particles are pushed in an opposite direction from the negative ones, leading to a zero net force on the object?

Also, I'm curious why the armature in the rail gun moves. How does it have a charge? I know electrons are moving through it, but there should be just as many entering it as leaving it at any given time. I would think that its net charge would be neutral.

Originally Posted by kojax

So, do positive and negative particles get pushed in the same direction or in opposite directions by the Lorentz force? Most matter is composed both of protons and electrons, so I'm trying to understand why neutrally charged objects don't move. Is it because the positive particles are pushed in an opposite direction from the negative ones, leading to a zero net force on the object?

Precisely. The Lorentz force equatin is a vector equation so the direction of the force exerted on a charged particle is determined by whether the charge is positive or negative.

Most material is, macroscopically, electrically neutral because the positive and negative charges are equal.

Originally Posted by kojax

Also, I'm curious why the armature in the rail gun moves. How does it have a charge? I know electrons are moving through it, but there should be just as many entering it as leaving it at any given time. I would think that its net charge would be neutral.

Rail guns, like ordinary electric motors are driven by magnetic fields and there are no net charges involved.

What happens is that a magnetic field induces eddy currents in a conductive material whih create a magnetic field that interacts with the original magnetic field and the forces are associated with these fields. You might find a book on electromagnetic machinery and read up on induction motors.

You can also envision the forces as those imposed on the moving charges that create the eddy currents, and that does follow the Lorentz force law. The reason for the forces in the electrically neutral materials is that the electrons are in motion while the positive charges are stationary. So only the moving charges feel the effect of the magnetic field.

Originally Posted by kojax

Also, I'm curious why the armature in the rail gun moves. How does it have a charge? I know electrons are moving through it, but there should be just as many entering it as leaving it at any given time. I would think that its net charge would be neutral.

A moving capacitor has a larger electric field that a still standing one. It says so here:

http://en.wikipedia.org/wiki/Relativ...ectromagnetism


The rails of a rail gun are partly moving. The electrons in the rails are moving.

Those moving electrons form a moving capacitor. In this capacitor the plates have
the same charge, and the plates repel each other with force that is increased by
the motion.

And that's why the rails repel each other.



Now that we understand how the rails repel, we can maybe figure out how the armature is
repelled. (Maybe this isn't so simple after all)

Originally Posted by jartsa

Originally Posted by kojax

Also, I'm curious why the armature in the rail gun moves. How does it have a charge? I know electrons are moving through it, but there should be just as many entering it as leaving it at any given time. I would think that its net charge would be neutral.

A moving capacitor has a larger electric field that a still standing one. It says so here:

http://en.wikipedia.org/wiki/Relativ...ectromagnetism


The rails of a rail gun are partly moving. The electrons in the rails are moving.

Those moving electrons form a moving capacitor. In this capacitor the plates have
the same charge, and the plates repel each other with force that is increased by
the motion.

And that's why the rails repel each other.



Now that we understand how the rails repel, we can maybe figure out how the armature is
repelled. (Maybe this isn't so simple after all)

I'm going to have to say I like Dr. Rocket's explanation better. I'm trying to understand this using Lorentz force as my sole perspective right now. Presumably all of the perspectives add up to the same conclusion, just approaching the same event from different angles.

If yours proves to be accurate then I'll probably examine it later, once I've managed to establish a more complete understanding from my preferred angle of approach.

Originally Posted by DrRocket

You can also envision the forces as those imposed on the moving charges that create the eddy currents, and that does follow the Lorentz force law. The reason for the forces in the electrically neutral materials is that the electrons are in motion while the positive charges are stationary. So only the moving charges feel the effect of the magnetic field.

So, using this perspective, would we be saying that the electrons feel the force more strongly than the protons because they are physically closer to the center of the magnetic (and probably also electric) fields they are generating by moving? This is very helpful in trying to understand what's happening. For example: this section of the wiki article on electrons was previously totally unapproachable to me. It is .....beginning..... to make more sense now......

http://en.wikipedia.org/wiki/Electron#Interaction

DrRocket we are talking about different rail gun. There were pictures back there on the previous page.

This rail gun is a telescopic electric circuit.

I'm pretty sure he's talking about the same one, Jartza. You have a very interesting perspective, and I'm not sure about its accuracy yet, but you should be careful trying to contradict established physics if you want to continue on this site for long. Most of relativity bases itself on the established understanding of electro-magnetism. If you want to make reference to it in your own explanations, then you can't go contradicting its underlying principles.


I'm pretty sure that every physicist in the world would agree with Dr. Rocket's explanation. He's helping me understand something that most trained physicists understand in detail. It's just not easy to understand when you're first trying to learn it, like I am.

Originally Posted by kojax

I'm pretty sure he's talking about the same one, Jartza. You have a very interesting perspective, and I'm not sure about its accuracy yet, but you should be careful trying to contradict established physics if you want to continue on this site for long. Most of relativity bases itself on the established understanding of electro-magnetism. If you want to make reference to it in your own explanations, then you can't go contradicting its underlying principles.


I'm pretty sure that every physicist in the world would agree with Dr. Rocket's explanation. He's helping me understand something that most trained physicists understand in detail. It's just not easy to understand when you're first trying to learn it, like I am.

Jartsa's perspective is highly inaccurate. you can disregard everything contained in all of his posts. Dr Rocket reverberated that point in this and other threads, and I feel it's safe to say he is the utmost authority on physics on the forum.

Originally Posted by kojax

I'm pretty sure he's talking about the same one, Jartza. You have a very interesting perspective, and I'm not sure about its accuracy yet, but you should be careful trying to contradict established physics if you want to continue on this site for long. Most of relativity bases itself on the established understanding of electro-magnetism. If you want to make reference to it in your own explanations, then you can't go contradicting its underlying principles.


I'm pretty sure that every physicist in the world would agree with Dr. Rocket's explanation. He's helping me understand something that most trained physicists understand in detail. It's just not easy to understand when you're first trying to learn it, like I am.

Well what can I do, I see a device where eddy currents are important, and I see another device
where eddy currents are not important.

I did read carefully the good explanation of one type of rail guns, in the page that kojax
pointed me to. I don't know if there are many types of rail guns...

Also coil guns were mentioned there. Coil guns of course are not rail guns. But they are are a
little bit like rail guns ...

Originally Posted by jartsa

Originally Posted by kojax

I'm pretty sure he's talking about the same one, Jartza. You have a very interesting perspective, and I'm not sure about its accuracy yet, but you should be careful trying to contradict established physics if you want to continue on this site for long. Most of relativity bases itself on the established understanding of electro-magnetism. If you want to make reference to it in your own explanations, then you can't go contradicting its underlying principles.


I'm pretty sure that every physicist in the world would agree with Dr. Rocket's explanation. He's helping me understand something that most trained physicists understand in detail. It's just not easy to understand when you're first trying to learn it, like I am.

Well what can I do, I see a device where eddy currents are important, and I see another device
where eddy currents are not important.

I did read carefully the good explanation of one type of rail guns, in the page that kojax
pointed me to. I don't know if there are many types of rail guns...

Also coil guns were mentioned there. Coil guns of course are not rail guns. But they are are a
little bit like rail guns ...

That is the only type of rail gun, which is why it is labeled "rail gun" as opposed to something else

Originally Posted by DrRocket

When a charged particle accelerates it also radiates an electromagnetic wave.

I'm a little confused on this issue. If every time you accelerate a charged particle, it then emits an EM wave and slows down again, then how would an electron ever increase its velocity? In order to speed up, doesn't it have to accept energy and then not re-emit it?

Or... is the emitting of the EM wave not slowing it down?

Originally Posted by jartsa

Well what can I do, I see a device where eddy currents are important, and I see another device
where eddy currents are not important.

I did read carefully the good explanation of one type of rail guns, in the page that kojax
pointed me to. I don't know if there are many types of rail guns...

Also coil guns were mentioned there. Coil guns of course are not rail guns. But they are are a
little bit like rail guns ...

I'm going to be sad to see you go Jartsa, but the other posters are right. You're trying to use your own inability to understand electromagnetism as an argument against someone's perspective who fully understands it. If you want to understand it better, then ask questions. Don't just make uninformed statements and then wait to be corrected.

Originally Posted by kojax

I'm going to be sad to see you go Jartsa, but the other posters are right. You're trying to use your own inability to understand electromagnetism as an argument against someone's perspective who fully understands it. If you want to understand it better, then ask questions. Don't just make uninformed statements and then wait to be corrected.

Well, you are really quite upset because of me saying to DrRocket "look at the picture there"

How did I dare do such a thing



What do you think about a ship loaded with bar magnets? Does it drift somewhere
because of those magnets?

Originally Posted by jartsa

Originally Posted by kojax

I'm going to be sad to see you go Jartsa, but the other posters are right. You're trying to use your own inability to understand electromagnetism as an argument against someone's perspective who fully understands it. If you want to understand it better, then ask questions. Don't just make uninformed statements and then wait to be corrected.

Well, you are really quite upset because of me saying to DrRocket "look at the picture there"

How did I dare do such a thing



What do you think about a ship loaded with bar magnets? Does it drift somewhere
because of those magnets?

It drifts because of ocean currents. There is a chance that a passing mass of iron could attract it, or rather, it attract the iron, but in general, it'll drift because of currents in the water and little else

Originally Posted by jartsa

Originally Posted by kojax

I'm going to be sad to see you go Jartsa, but the other posters are right. You're trying to use your own inability to understand electromagnetism as an argument against someone's perspective who fully understands it. If you want to understand it better, then ask questions. Don't just make uninformed statements and then wait to be corrected.

Well, you are really quite upset because of me saying to DrRocket "look at the picture there"

How did I dare do such a thing



What do you think about a ship loaded with bar magnets? Does it drift somewhere
because of those magnets?

No, I'm not upset because you said it, not exactly. It's just that it was very clear that he was quite certainly talking about the picture. The armature moves because the electric current flowing through it is perpendicular to the magnetic field near it. Dr. Rocket only needed to add one thing to make it clear why the armature moves: what makes it behave like it has a charge? And he did, and his answer made sense.

I usually like to keep my mind open to a wide variety of perspectives, but .... electromagnetic theory is highly tested by experiment. There's very little room to doubt its accuracy at this point in history. It's not a "theory" in the same sense as say .... the Big Bang Theory.

Originally Posted by jartsa

Originally Posted by kojax

Also, I'm curious why the armature in the rail gun moves. How does it have a charge? I know electrons are moving through it, but there should be just as many entering it as leaving it at any given time. I would think that its net charge would be neutral.

A moving capacitor has a larger electric field that a still standing one. It says so here:

http://en.wikipedia.org/wiki/Relativ...ectromagnetism


The rails of a rail gun are partly moving. The electrons in the rails are moving.

Those moving electrons form a moving capacitor. In this capacitor the plates have
the same charge, and the plates repel each other with force that is increased by
the motion.

And that's why the rails repel each other.



Now that we understand how the rails repel, we can maybe figure out how the armature is
repelled. (Maybe this isn't so simple after all)

\


This could not possible be more wrong. A moving capacitor does NOT have an increased electric field as opposed to a stationary one. Moreover, for the phenomenon of interest here the electric field is totally irrelelvant.

The rails do NOT form a moving capacitor. In fact, they are electrically neutral, which quite the opposite of what one finds in a capacitor.

The repulsion between the two current-carrying rails is due entirely to the effect of the magnetic fields created by the currents on the current-carrying electrons that create the current. The repulsion is NOT due to the electric field E, which is what is operative in a capacitor, but rather to the magnetid B field which results from the current.

In short, you have the physics completely wrong. As usual.

For chrissake, go read a decent book on electromagnetism.

Originally Posted by DrRocket

The repulsion between the two current-carrying rails is due entirely to the effect of the magnetic fields, created by the currents, on the current-carrying electrons that create the current.

I knew that. (I added two commas there, for clarity)


Eddy currents have nothing to do with this, right?

Originally Posted by Arcane_Mathematician

Originally Posted by jartsa

What do you think about a ship loaded with bar magnets? Does it drift somewhere
because of those magnets?

It drifts because of ocean currents. There is a chance that a passing mass of iron could attract it, or rather, it attract the iron, but in general, it'll drift because of currents in the water and little else

Why is it that magnetic field of earth does not cause any drifting, but magnetic field of mass of iron
does?

Originally Posted by kojax

The armature moves because the electric current flowing through it is perpendicular to the magnetic field near it. Dr. Rocket only needed to add one thing to make it clear why the armature moves: what makes it behave like it has a charge? And he did, and his answer made sense.

Can you explain it to me?

Originally Posted by jartsa

Originally Posted by kojax

The armature moves because the electric current flowing through it is perpendicular to the magnetic field near it. Dr. Rocket only needed to add one thing to make it clear why the armature moves: what makes it behave like it has a charge? And he did, and his answer made sense.

Can you explain it to me?

Nope.

You lack the capability to understand.

Originally Posted by jartsa

Originally Posted by kojax

The armature moves because the electric current flowing through it is perpendicular to the magnetic field near it. Dr. Rocket only needed to add one thing to make it clear why the armature moves: what makes it behave like it has a charge? And he did, and his answer made sense.

Can you explain it to me?

It's good now you are asking questions, at least, instead of making statements.

Lorentz force follows the right hand rule I posted on the other page. The magnetic field between the rails is up and down because of another right hand rule. The magnetic field around a wire with electric current is always up facing on the left hand side of a wire, and faces down on the right hand side.

Clearly the electric current flowing through the armature is flowing from right to left. If the Magnetic field is going up, and the electric field is going left, then the Lorentz force pushes forward.

Originally Posted by kojax

Originally Posted by jartsa

Originally Posted by kojax

The armature moves because the electric current flowing through it is perpendicular to the magnetic field near it. Dr. Rocket only needed to add one thing to make it clear why the armature moves: what makes it behave like it has a charge? And he did, and his answer made sense.

Can you explain it to me?

It's good now you are asking questions, at least, instead of making statements.

Lorentz force follows the right hand rule I posted on the other page. The magnetic field between the rails is up and down because of another right hand rule. The magnetic field around a wire with electric current is always up facing on the left hand side of a wire, and faces down on the right hand side.

Clearly the electric current flowing through the armature is flowing from right to left. If the Magnetic field is going up, and the electric field is going left, then the Lorentz force pushes forward.

There is no electric field (i.e. the field is 0) in the case of a steady-state DC current. There is only the magnetic field -- the problem is one of magnetostatics. But the magnetic field is all that is needed, and in combination with the Lorentz force equation explains what is going on, as noted earlier.

Ok, so there are four concepts now. Electric Field, Electric Force, Electric Current, and Electric Potential.

I think I had electric potential and electric field confused here. Clearly an electric potential exists between the right and left sides of the armature, or there wouldn't be any current flowing through it. (I mean right and left from the perspective of if someone is standing behind it, holding the rail gun upright.)

Are electric fields then what happens when an object has a net charge? And, I guess electric force would be what attracts a positively charged object to a negatively charged object?

Originally Posted by kojax

Ok, so there are four concepts now. Electric Field, Electric Force, Electric Current, and Electric Potential.

I think I had electric potential and electric field confused here. Clearly an electric potential exists between the right and left sides of the armature, or there wouldn't be any current flowing through it. (I mean right and left from the perspective of if someone is standing behind it, holding the rail gun upright.)

Are electric fields then what happens when an object has a net charge? And, I guess electric force would be what attracts a positively charged object to a negatively charged object?

An electric potential is a scalar field the gradient of which is the electric field. Only a conservative field can be the gradient of a scalar, so only electrostatic fields arise in this way. Time varying fields do not (the idea can be extended to a so-called vector potential but that is a somewhat different wrinkle).

An electric force is the force that is exerted on a charged particle by an electric field. It is described by the Lorentz force equation (with the magnetic field being zero).

Electric current is the result of movement of charged particles. In field theory the movement of the particles results in current density and the crossing a surface is determined by an integral of the current density over the surface. A current in a conductive material can exist even though the net charge in the material is zero --- as in the case of ordinary current in a wire.

There is a challenge from Australian engineer that I have published on my website.
One person already took a challenge to build his device that is based on magnetic motion. He is communicating with Hans directly. On Tuesday, 28th I will publish his drawings of that device and I invite you to look his view on magnetism.
Right now you can go on my website Real People Real Answers (com.au) and read his first publication under Experts page.
I would welcome every possible opinion!

warmest regards

Originally Posted by DrRocket

Originally Posted by kojax

Ok, so there are four concepts now. Electric Field, Electric Force, Electric Current, and Electric Potential.

I think I had electric potential and electric field confused here. Clearly an electric potential exists between the right and left sides of the armature, or there wouldn't be any current flowing through it. (I mean right and left from the perspective of if someone is standing behind it, holding the rail gun upright.)

Are electric fields then what happens when an object has a net charge? And, I guess electric force would be what attracts a positively charged object to a negatively charged object?

An electric potential is a scalar field the gradient of which is the electric field. Only a conservative field can be the gradient of a scalar, so only electrostatic fields arise in this way. Time varying fields do not (the idea can be extended to a so-called vector potential but that is a somewhat different wrinkle).

I had always assumed that the electrical component of an EM wave was just an electric potential. So at any given moment when the electric field appeared to be positive if measured from the left hand side, it would appear to be negative if measured from the right hand side.

Is that incorrect? Is the electric field positive on both sides, then negative on both sides, instead of being positive/neg, then negative/pos like I've been visualizing it?

Originally Posted by kojax

Originally Posted by DrRocket

Originally Posted by kojax

Ok, so there are four concepts now. Electric Field, Electric Force, Electric Current, and Electric Potential.

I think I had electric potential and electric field confused here. Clearly an electric potential exists between the right and left sides of the armature, or there wouldn't be any current flowing through it. (I mean right and left from the perspective of if someone is standing behind it, holding the rail gun upright.)

Are electric fields then what happens when an object has a net charge? And, I guess electric force would be what attracts a positively charged object to a negatively charged object?

An electric potential is a scalar field the gradient of which is the electric field. Only a conservative field can be the gradient of a scalar, so only electrostatic fields arise in this way. Time varying fields do not (the idea can be extended to a so-called vector potential but that is a somewhat different wrinkle).

I had always assumed that the electrical component of an EM wave was just an electric potential. So at any given moment when the electric field appeared to be positive if measured from the left hand side, it would appear to be negative if measured from the right hand side.

Is that incorrect? Is the electric field positive on both sides, then negative on both sides, instead of being positive/neg, then negative/pos like I've been visualizing it?

The electric component of an electromagnetic wave is NOT an electric potential. It is a vector field and it is not conservative in any case. See earlier post.

You might also be interested to know that the electric and magnetic components of al electromagnetic wave are not invariant of the observer. This is a consequence of special relativity.

I think you need to read a good book on electromagnetism. See earlier posts for some recommendations.

Originally Posted by kojax

I had always assumed that the electrical component of an EM wave was just an electric potential. So at any given moment when the electric field appeared to be positive if measured from the left hand side, it would appear to be negative if measured from the right hand side.

Is that incorrect? Is the electric field positive on both sides, then negative on both sides, instead of being positive/neg, then negative/pos like I've been visualizing it?

Take a small piece of some charged object's electric field. That's what's it's like.

Originally Posted by jartsa

Originally Posted by kojax

I had always assumed that the electrical component of an EM wave was just an electric potential. So at any given moment when the electric field appeared to be positive if measured from the left hand side, it would appear to be negative if measured from the right hand side.

Is that incorrect? Is the electric field positive on both sides, then negative on both sides, instead of being positive/neg, then negative/pos like I've been visualizing it?

Take a small piece of some charged object's electric field. That's what's it's like.

rubbish

Originally Posted by kojax

Magnetic fields can't move things on their own, right? Magnetized objects push and pull off of each other, but all the magnetic field does is decide what state of magnetism an object will experience? A single piece of metal, placed in a magnetic field, would not begin moving until another object enters the area for it to act on/be acted on?

In electromagnetic terms a magnetic field cannot generate a force by itself. What you need is the interaction of two magnetic fields. Attractive forces are produced when the energy in the combined field is lower than the sum of the energy in the two fields when separated.

An object may interact with a magnetic field, and be pulled into it or repelled from it, depending on the nature of the material and the shape of the magnetic field. However, if the magnetic field has no particular gradient it may not move or experience any forces, or may be trapped in a magnetic bottle, even though interacting with the field and changing its energy distribution.