# Basic question on magnetism regarding north and south pole

I am currently busy with some magnetism and quite shockingly (to me at least) I haven't yet read anything about the difference between the north pole and the south pole of a magnet. Before I started with magnetism I learned electricity, here there 2 opposite charges: negative charges (electrons) and positive charges (protons). Although I know for the people on this forum, that is very rudimentary, I at least find at a satisfactory explanation; different particles have different charges; a positive or a negative one. With magnetism I haven't stumbled across this yet.

• My teacher told me you can't say there is a positive and negative 'magnetic charge' (I don't know how to call it); but why?

• Also, what causes the difference between the 2?

• And, now that I'm thinking about it; are there actually magnets with only a north pole or a south pole (if not, why are the 2 so fundamentally connected that you can't have one without the other)?

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Sorry if these questions seem too rudimentary, but high school physics annoys me often with these types of things; just a set of formulas, calculate this and that, without actually explaining why and how it works. Luckily I have this site! – user14445 Jan 8 '13 at 20:55
You show in your question that you really think about the physics. The question is also clear and well-written. The people on this website are very happy to answer these kind of questions! – Bernhard Jan 16 '13 at 18:16

Your teacher's statement that you can't talk about positive and negative magnetic charge is ... difficult.

You see, there have been no observations of any magnetic charges (which are called "magntic monopoles"), but a lot of theorists favor the existence of such criters because

• it has the very elegant and satisfing result of explaining why electric charge must be quantized
• the mathematics of electomagnetism are nearly symmetric between electric and magnetic phenomena and adding magnetic monopoles would make them fully symmetric

If there are magnetic monopoles then they would comes in positive and negative varieties, and even though they are not monopoles the difference between the poles of a magnetic is very much the same as the difference between positive and negative electric charges.

To illustrate what I mean by the difference being like that between charge polarities, consider that electric field lines are seen as coming "out" of positive charges and going "in" to negative charges. Likewise--if we don't look inside the magnet--magnetic field lines are drawn going "out" from the north pole and "in" to the south pole. (Looking inside the magnet the situation is reverse, because in the absence of monopoles all magnetic field lines are loops, but I don't want to get into that.)

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But what causes this difference? Or is this not as simple as the difference between a positive and negative charge? – user14445 Jan 8 '13 at 21:00
In both cases (positive and negative charge and north or south poles) the assignment is really quite arbitrary and we could reverse the assignment by changing the sign of terms related to that particular field in some basic equations. – dmckee Jan 8 '13 at 21:05

North and south poles of a magnet were defined at a time when there was no theory to explain them, but people had observed that some iron rods oriented themselves always towards the north south axis with one side pointing north consistently, so they named the poles. As the link says now one can define the poles by the right hand rule, since one can have a magnetic field from current carrying wires.

In elementary particle experimental studies no magnetic monopoles have been found, not for lack of trying. There does not exist a single north or a single south pole, as one finds with charges.

And, [k]now that I'm thinking about it; are there actually magnets with only a north pole or a south pole (if not, why are the 2 so fundamentally connected that you can't have one without the other)?

No, there do not exist such separated poles, although human ingenuity can simulate such poles by concentrating the magnetic field lines at one pole and geometrically distributing the other field lines so that the field is locally very weak there.

Magnets are at least dipoles . Naturally found iron magnets have tiny dipoles lined up inside to create the macroscopic external magnetic field.

In order for monopoles to play the same role as electrons, as is implied in your question,they would have to exist and be as numerous as electrons. This evidently is not the case as no magnetic monopoles have been observed in all the data up to now. Theories abound, your expectation is a sort of theory, but until there exist data validating the theories we cannot be speaking of monopoles as existing. They are hypothetical particles.

If you want a correspondence with electric charges it is the electric dipoles that are the analogue for the magnetic dipole. Many atoms and molecules have these electric dipole moments they are not as attractive or repulsive as bare electron charges, but still they are important for the structure of matter and its chemical properties.

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I don't know why my age is relevant, so I don't state it in my profile. Also, my physics background is not huge, I'm still in high school. I read the wikipedia article in my native language before consulting this site, and it showed nothing of use (Dutch if you're feeling pessimistic). – user14445 Jan 8 '13 at 21:08
@user14445 Your age and preparation are only relevant insofar as they help us write answers that will be useful to you. You are not required to provide such information but doing so might get you better answers. – dmckee Jan 8 '13 at 21:09
Well, age helps to know that you are in high school without having to ask. One answers differently to a 70 year old asking the same question than to a student. – anna v Jan 8 '13 at 21:10
@annav Well in that case, you could have seen the comment below my question (which predates your answer) and see that I'm in high school. Also, I referred to my educator as 'teacher', not 'professor'; this could have also helped you. – user14445 Jan 8 '13 at 21:11
Right , but it is a guess. There are a number of students of mature years nowadays. – anna v Jan 8 '13 at 21:14

In an plug outlet there is one 'hot' side (the skinny one) and a neutral (equivalent to the ground - and it's the fatter one).

The hot side is negatively charged because the electrons come from there and travel basically anywhere else, but wants to go to the positive side.

Now alternating current flows from the negative side but it's called Alternating because one is North and the other South.

If a north electron is heading toward you, you will see it spinning like a bullet clockwise. If a south electron is heading toward you, you will see it spinning like a bullet counter-clockwise.

They repel because each is trying to spin the other the opposite way.

Picture a straw with one end marked "North" and the other "South". Next mark a direction on the outside of it. At the bottom, mark an arrow going to the left. At the top mark an arrow to points the same way. Now look down the straw. From South to North you will see the directions are both facing counter-clockwise. From North to South you will see the directions are both facing clockwise.

Tesla discovered that by alternating the poles of the magnet if will naturally repel down the line.

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