Mr Skeptic Posted December 2, 2009 Posted December 2, 2009 a.) monopole has only one pole, only one center of origin b.) strength of monopole decreases with distance by inverse-square law c.) finally, to avoid confusion, strength of dipole decreases with distance by inverse-cube law Fair enough, and the field of it as I said will be lines going toward or away from the monopole. The lines going in circles that you show would cause no force toward your supposed monopole, rather in circles around it. Simply said, monopole is what you get when you split dipole in half, like this: But that's not even half of the dipole's field. The dipole is cylindrically symmetrical, and the 3D field of it looks like concentric donuts. The field of the infinitely long wire would look like concentric cylinders. Furthermore, for the wire the strength of the field depends on the distance from the wire so the 2D circles are centered on the wire. For the dipole, the strength depends on the distance from the dipole, so the circles in 2D are closer together near the dipole and farther from each other away from it. To get half the field like you are trying to do is simple enough. All you have to do is set a magnet on a superconductor (the superconductor will exclude the magnetic field). Won't stop it from having a north and south pole though. Regardless, to get a monopole what you need to do is cut the field in half the other direction. You do realize that the entire side where the field lines are leaving is north and the side where the field lines are entering is south, right? The way you suggest cutting it you get half the north and half the south poles.
bigbadjesus Posted December 2, 2009 Posted December 2, 2009 Cutting them in half does not give you two monopoles. Why not? just to clarify, I know why not, but since this is a science forum, maybe you want to give a reason behind something instead of just saying 'this is so'
ajb Posted December 2, 2009 Posted December 2, 2009 (edited) Why not? just to clarify, I know why not, but since this is a science forum, maybe you want to give a reason behind something instead of just saying 'this is so' Cutting an infinite wire in half will just give you two infinite wires! One could also think about cutting a bar magnet on half. Try it Fundamentally, this all comes down to Gauss' law again. No magnetic charges, no separate North and South poles. All magnetism we see comes from the motion of electric charges. The magnetic field associated with such motion are necessarily closed loops (or going off to infinity and returning again). Cutting magnet in half only creates two lots of these loops, not an isolated pole. Edited December 2, 2009 by ajb
swansont Posted December 2, 2009 Posted December 2, 2009 I would define monopole normally, like they are defined: a.) monopole has only one pole, only one center of origin b.) strength of monopole decreases with distance by inverse-square law c.) finally, to avoid confusion, strength of dipole decreases with distance by inverse-cube law The field of an infinite wire drops off as 1/r.
npts2020 Posted December 2, 2009 Posted December 2, 2009 Sha31; Even the diagram you have shown has a + and - marked on the wire, isn't that an indication the presence of a dipole?
Mr Skeptic Posted December 2, 2009 Posted December 2, 2009 Sha31; Even the diagram you have shown has a + and - marked on the wire, isn't that an indication the presence of a dipole? That just marks the direction of the current in the wire. However, the circular magnetic field lines he shows have both a magnetic field line entering and leaving each point, which he still does not realize means it can't be a monopole (which have field lines only entering or leaving).
Sha31 Posted December 2, 2009 Author Posted December 2, 2009 (edited) Sha31; Even the diagram you have shown has a + and - marked on the wire, isn't that an indication the presence of a dipole? That is electric polarity, indicating direction of electrons in the wire. You see how magnetic dipole looks like, right? So, where is the second MAGNETIC pole in that other picture? Merged post follows: Consecutive posts mergedThat just marks the direction of the current in the wire. However, the circular magnetic field lines he shows have both a magnetic field line entering and leaving each point, which he still does not realize means it can't be a monopole (which have field lines only entering or leaving). What are you talking about? It is the same thing with dipole lines, even if you consider the field lines of only one pole you will get DIRECTION at any point i.e. magnetic field line entering and leaving each point. Why are you surprised magnetic monopoles would behave exactly as on of the magnetic dipole poles? Why does that magnetic field looks like only half of dipole, why does it not look like normal dipole? How do you know dipole field lines do not circle around these two poles? Why do you think magnetic dipole field lines go through the poles exactly? Merged post follows: Consecutive posts mergedThe field of an infinite wire drops off as 1/r. Where did you get that? It drops of as 1/r^2. http://en.wikipedia.org/wiki/Biot-savart Just like Newton's gravity and Coulomb's law. This should finally confirm how magnetic moment of a moving charge is actually monopole. Edited December 2, 2009 by Sha31 Consecutive posts merged.
Mr Skeptic Posted December 2, 2009 Posted December 2, 2009 So, where is the second MAGNETIC pole in that other picture? So, where's the first magnetic pole on it? What are you talking about? It is the same thing with dipole lines, even if you consider the field lines of only one pole you will get DIRECTION at any point. Why are you surprised magnetic monopoles would behave exactly as on of the magnetic dipole poles? Why does that magnetic field looks like only half of dipole, why does it not look like normal dipole? What direction are you supposedly cutting the field in half? Do you end up with only one pole or half of each? I think that in your other picture you confused where the poles are. Note how at each pole the field lines are moving away from each other kind of like they would for a monopole, but only on one side. On the other side they don't look like a monopole. And one more thing. Electric and magnetic fields are 3D vector fields. As field lines the direction of the line shows the direction of the vector and how close to each other the lines are shows its strength. You seem to be under the impression that the field lines are 2D. They are not, they are 3D. But since the field of these simple objects is symmetrical, you should be able to figure out what the shape of the 3D field is.
Sha31 Posted December 2, 2009 Author Posted December 2, 2009 So' date=' where's the [i']first[/i] magnetic pole on it? Very close to where the field magnitude is the strongest, of course. What did you think? This works for gravity monopoles, electric monopole, for magnetic dipoles, and is therefore the definition of how to find a pole... then you can count them. What direction are you supposedly cutting the field in half? Do you end up with only one pole or half of each? I think that in your other picture you confused where the poles are. Note how at each pole the field lines are moving away from each other kind of like they would for a monopole' date=' but only on one side. On the other side they don't look like a monopole. And one more thing. Electric and magnetic fields are 3D vector fields. As field lines the direction of the line shows the direction of the vector and how close to each other the lines are shows its strength. You seem to be under the impression that the field lines are 2D. They are not, they are 3D. But since the field of these simple objects is symmetrical, you should be able to figure out what the shape of the 3D field is.[/quote'] 3D topology has nothing to with the number of poles. I'm not cutting anything. Clearly the image depicting dipole magnetic fields shows TWO sets of circles, whether they are contours of torus, ball or whatever, this other picture shows only ONE set of circles, hence this very logical and straight forward conclusion. If it is dipole, then where is the second set of circles?
swansont Posted December 2, 2009 Posted December 2, 2009 Where did you get that? It drops of as 1/r^2. http://en.wikipedia.org/wiki/Biot-savart That's the equation you have to apply, but you need to integrate it over the length of the wire, because all of the current contributes to the field at any given point. When you do, you get [math]\frac{\mu_0 I}{2\pi r}[/math]
Sha31 Posted December 2, 2009 Author Posted December 2, 2009 That's the equation you have to apply, but you need to integrate it over the length of the wire, because all of the current contributes to the field at any given point. When you do, you get [math]\frac{\mu_0 I}{2\pi r}[/math] Where did you get that from? What equation is that? If you take equation for point charges, either for magnetic or electric potential, you will see it drops with 1/r^2, so forget the wire for whatever efect that might have on compound field strength, consider just one electron, i.e. just one electric and one magnetic field. Merged post follows: Consecutive posts merged The lines going in circles that you show would cause no force toward your supposed monopole, rather in circles around it. No. This magnetic force is perpendicular to magnetic field. It actually acts directly toward the monopole origin i.e. electron. http://en.wikipedia.org/wiki/Lorentz_force Can we finally agree and can I get some prize for this discovery now?
Mr Skeptic Posted December 2, 2009 Posted December 2, 2009 If it is dipole, then where is the second set of circles? What second set of circles? A dipole does not have a "second set of circles". It has an infinite set of concentric toroids (donut shape). Look again at the magnet picture and tell me if the poles are where the circles are or where the field lines are getting farther apart the farther you get from them? Merged post follows: Consecutive posts mergedCan we finally agree and can I get some prize for this discovery now? What's the prize for misunderstanding something that has been well-known for longer than you've been alive? Merged post follows: Consecutive posts mergedAt this point, it is useless to talk theory to you. Go, get a wire, a 12 volt battery, and a magnet. Knock yourself out. Here's a thought: is your supposed magnetic monopole a north magnetic monopole or a south magnetic monopole? Easy way to tell, does it attract or repel the north pole of a magnet? Other easy way to tell: does it attract or repel itself? Or, does that depend on the orientation? If you like, you can save yourself some money by looking up the force of magnetic attraction between wires (and that it depends on orientation).
Cap'n Refsmmat Posted December 3, 2009 Posted December 3, 2009 Where did you get that from? What equation is that? If you take equation for point charges, either for magnetic or electric potential, you will see it drops with 1/r^2, so forget the wire for whatever efect that might have on compound field strength, consider just one electron, i.e. just one electric and one magnetic field. But it's different for a wire vs. a point charge. You can't just assume a wire acts like a point charge.
Sha31 Posted December 3, 2009 Author Posted December 3, 2009 (edited) But it's different for a wire vs. a point charge. You can't just assume a wire acts like a point charge. You're right about assumptions, I agree, but it turns out it's all very similar whether you have two free electrons or bunch electrons together with protons and neutrons in some wire. You can model either case with the difference that free electrons experience more electrostatic repulsion, while when modeling wire protons would mostly neutralize this electric repulsion, but then you would have extra mass from these protons and neutrons. In any case Lorentz force equation would give you correct prediction of trajectories for free charges, electron beams, electrons inside a wire and even plasma. Merged post follows: Consecutive posts merged What second set of circles? A dipole does not have a "second set of circles". It has an infinite set of concentric toroids (donut shape). Do you not see two set of circles? What are you doing? Are you blind' date=' hypnotized... what? Look again at the magnet picture and tell me if the poles are where the circles are or where the field lines are getting farther apart the farther you get from them? Depends, of course, how you define a pole. Can you tell me where is the south and north pole fields strongest? Can you locate these two points and let me know where they are, approximately? That's where poles should be. What's the prize for misunderstanding something that has been well-known for longer than you've been alive? Let's see' date=' magnetic moment of a moving charge... a.) has only one pole b.) magnitude of the field drops with the distance by 1/r^2 c.) direction of the force is directed towards this one pole Yet, you say it's a... what? What do you say? Is it a dipole or what? Go, get a wire, a 12 volt battery, and a magnet. Here's a thought: is your supposed magnetic monopole a north magnetic monopole or a south magnetic monopole? Easy way to tell, does it attract or repel the north pole of a magnet? Other easy way to tell: does it attract or repel itself? Or, does that depend on the orientation? If you like, you can save yourself some money by looking up the force of magnetic attraction between wires (and that it depends on orientation). Right now I have only a DC transformer giving 5V, 4.5A and small permanent magnet, but I can not make wire move. You say it's easy, so tell us please: - Does magnetic field of a current carrying wire attract or repel north pole or south pole of a magnet, both or neither? Edited December 3, 2009 by Sha31 Consecutive posts merged.
Mr Skeptic Posted December 3, 2009 Posted December 3, 2009 Do you not see two set of circles? What are you doing? Are you blind, hypnotized... what? No. I see concentric toroids. That's a 3D shape in case you were wondering. Depends, of course, how you define a pole. Can you tell me where is the south and north pole fields strongest? Can you locate these two points and let me know where they are, approximately? That's where poles should be. As I told you, the strength of the magnetic field is shown as the density of the field lines. The field will be stronger where the field lines are close together. Incidentally, what do you think the N and S on that bar magnet stand for? Let's see, magnetic moment of a moving charge... a.) has only one pole b.) magnitude of the field drops with the distance by 1/r^2 c.) direction of the force is directed towards this one pole Yet, you say it's a... what? What do you say? Is it a dipole or what? I say it is the magnetic field of an infinitely long wire. It has no poles. It also does not follow 1/r^2, it follows 1/r. So by your own admission you too say it is not a pole. So where is the problem? Right now I have only a DC transformer giving 5V, 4.5A and small permanent magnet, but I can not make wire move. You say it's easy, so tell us please: - Does magnetic field of a current carrying wire attract or repel north pole or south pole of a magnet, both or neither? OK, just be careful not to make a short circuit, nor let your wire heat up too much. Actually, you do have to make a closed circuit, but what you need is for there to be enough resistance (a long enough wire or a resistor), then you can get away with that. If the resistance is too low your closed circuit is also a short circuit and you might melt wires or blow fuses. With 5 V you might not get much of a magnetic field. A single straight wire does not have much of a field. To make a stronger electromagnet, wrap a wire (insulated of course) several times around an iron nail. This will act as a bar magnet, and if it does not you probably don't have current. From the strength of that you can get an idea of how much less strong the single straight wire will be. Anyhow, your magnetic field should be stronger than that of the earth (but if it is not then you won't have much luck). As for your permanent magnet, do you know where the poles on it are? If not you can float it on a piece of styrofoam or aluminum foil boat. The earth's magnetic field should align the magnet so the north pole points north, unless you put the magnet in with the pole pointing downward or it has a funny shape. Incidentally, the earth's magnetic north is on the south pole and the earth's magnetic south at the north pole. To increase the sensitivity of your experiment, you can float your magnet on water or tie it on a long string. Note that in water surface tension can be much stronger than you might think. Now, to determine what the effect will be of the magnetic field of a straight wire (well technically you have to make a loop but if you are close to the wire and the loop is fairly large, it will be very similar) will have on a magnet. Now, magnets align in the direction of the magnetic field. Putting a magnet near the wire will result in a torque until the magnet is perpendicular to the wire. If you let it turn, there will be attraction between the wire and the magnet. If instead you turn the magnet the opposite direction than it "wants" to go, you will get repulsion. So it won't attract the pole but rather a side of your magnet.
Sha31 Posted December 3, 2009 Author Posted December 3, 2009 (edited) Magnetic moment of a moving charge... What do you say? Is it a dipole or what? It has no poles. Hmm? Magnetic nopole?! It also does not follow 1/r^2' date=' it follows 1/r. [/quote'] Not really. What formula are you talking about? Where did you find that information? It follows 1/r^2, juts like other monopoles, such as gravity and electric fields. Point charge at constant velocity http://en.wikipedia.org/wiki/Biot-savart So it won't attract the pole but rather a side of your magnet. Is that from some text-book' date=' or just your 'gut feeling', perhaps experimental observation? As I told you, the strength of the magnetic field is shown as the density of the field lines. The field will be stronger where the field lines are close together. Let me show you something... http://my.execpc.com/~rhoadley/field01.htm TWO WIRES This shows the field around two wires, side by side, that are carrying current in opposite directions. DISK MAGNET This shows the field lines around a disk magnet where the North pole is at the top. This shows the magnetic field strength around the disk magnet. It is strongest in the corners, not in the center of the poles! Edited December 3, 2009 by Sha31
swansont Posted December 3, 2009 Posted December 3, 2009 Where did you get that from? What equation is that? I got that from the Biot-Savart Law, when applied to an infinite wire. Just as I already said. It's worked out in most physics textbooks that discuss E&M, and makes you appreciate the tricks that let you use symmetry to derive the same equation (Ampere's Law) If you take equation for point charges, either for magnetic or electric potential, you will see it drops with 1/r^2, so forget the wire for whatever efect that might have on compound field strength, consider just one electron, i.e. just one electric and one magnetic field. But not if you take the system and transform it into a moving coordinate system, which is what you're doing. The definitions we are using are meant for a charge or magnet configuration at rest, not one that is moving, which changes it. Can we finally agree and can I get some prize for this discovery now? Umm, no.
ajb Posted December 3, 2009 Posted December 3, 2009 Can we finally agree and can I get some prize for this discovery now? Time to lock this thread?
Mr Skeptic Posted December 3, 2009 Posted December 3, 2009 Sha31, as I said I am through talking theory to you. Now, I told you how to set up your experiment, have fun with your wires and magnets. Then when you realize what we've been telling you is true, maybe we'll have more to talk about.
insane_alien Posted December 3, 2009 Posted December 3, 2009 notice how a wire looks similar to half of the magnet if you split it down the middle vertically. where you end up with a chunk of the north pole and the south pole? so even by your own logic a wire cannot be a monopole.
Sha31 Posted December 3, 2009 Author Posted December 3, 2009 I got that from the Biot-Savart Law, when applied to an infinite wire. You got it wrong then. Biot–Savart law http://en.wikipedia.org/wiki/Biot-savart The Biot–Savart law is used to compute the magnetic field generated by a steady current, i.e. a continual flow of charges, for example through a wire, which is constant in time and in which charge is neither building up nor depleting at any point. The equation is as follows: If the current has some thickness, the proper formulation of the Biot–Savart law (again in SI units) is: In the special case of a constant, uniform current I, the magnetic field B is: These equations are called the "Biot–Savart law for a point charge": But not if you take the system and transform it into a moving coordinate system' date=' which is what you're doing. The definitions we are using are meant for a charge or magnet configuration at rest, not one that is moving, which changes it. [/quote'] As explained in Wikipedia article these equations are for moving charges and currents. Since the magnitude depends on velocity there would not be any magnetic field if these charges were not moving. It's even called "magnetic field of MOVING charge". Magnetic field due to moving charges and electrical currents http://en.wikipedia.org/wiki/Magnetic_field#Magnetic_field_due_to_moving_charges_and_electrical_currents (Main articles: Electromagnet, Biot-Savart law, and Ampère's law) Have you noticed someone said this magnetic field has no poles? Usually, 'pole' is define as the point where the field magnitude is strongest. So, how would you define "pole" and how many poles do you think magnetic field of moving charge has? None, one, two, many?
Mr Skeptic Posted December 3, 2009 Posted December 3, 2009 In the special case of a constant, uniform current I, the magnetic field B is: So take the integral of that then, given an infinitely long wire, and you'll have your answer. You'll see that the relation to distance from the wire will be 1/r, just as your equation says it will. What this shows is just that you don't know how to do calculus, but we all already guessed that.
Sha31 Posted December 3, 2009 Author Posted December 3, 2009 Sha31, as I said I am through talking theory to you. Now, I told you how to set up your experiment, have fun with your wires and magnets. Then when you realize what we've been telling you is true, maybe we'll have more to talk about. Ok, I used car battery this time and I confirmed only one pole. Now, can you do it yourself and tell us: - does magnetic field of a current carrying wire attract or repel north pole or south pole of a permanent magnet, both or neither? Can you support your claim about "magnetic NO POLE"? How do you define 'pole'?
insane_alien Posted December 3, 2009 Posted December 3, 2009 a current carrying wire in a magnetic field will move perpendicularly to both the magnetic field and the electrical current.
Sha31 Posted December 3, 2009 Author Posted December 3, 2009 So take the integral of that then, given an infinitely long wire, and you'll have your answer. You'll see that the relation to distance from the wire will be 1/r, just as your equation says it will. What this shows is just that you don't know how to do calculus, but we all already guessed that. Show me your calculus or reference, you're imagining things. I'm talking about MONOPOLE, single charge, not infinite wire, ok? Magnetic filed of a single moving charge drops off as 1/r^2. YES/NO?
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