# What makes north pole of a magnet north pole in the first place? [duplicate]

This question might seem absurd and illogical to many. But it just popped out in my mind while I was reading about magnetism.

-Like in case of charges, positive and negative charge on an atom means absence and presence of extra electrons respectively. So my question is what aspect exactly makes a pole of magnet north or south? Is it absence or presence of something?

-I asked my teacher about this and he simply replied that north pole is something which attracts south pole. But this is more of a property to me rather than an exact meaning of what exactly is north pole of a magnet.

• – user207455 Jun 23 '19 at 8:34
• @Solar Mike all these answers in the question you recommended talk about properties or behaviour of magnet. Can you please presicely tell if there are any sort of particle involved which results in such behaviour of poles of magnets? – Garima Jun 23 '19 at 8:55
• Garima, as the answers in the question Solar Mike linked indicate, magnetism is related to the angular momentum of charges. So the North-South thing is ultimately related to the direction that the spin axis is pointing. – PM 2Ring Jun 23 '19 at 11:09
• This video may give you a partial answer. The video is specifically about electromagnets. Permanent magnets would (presumably) work in a similar way that I don't have the physics background to explain. (Therefore submitting this as a comment and not an answer.) youtube.com/watch?v=1TKSfAkWWN0 – Syntax Junkie Jun 23 '19 at 17:09

It is history, and it is worse than you think. North pole was defined as the pole that was attracted to the geological north of the earth. Compasses were very important to the sailors sailing the oceans.

A compass is a magnetic dipole, as magnetic monopoles do not exist as far as we know experimentally. This means that the geological magnetic dipole is defined the opposite than the compass dipole, since it must be the south that is drawn to the north.

Anyway, the answer is: a definition of the magnetic dipole as seen in magnetic materials. See the analogy with the electric dipole in my answer here.

• This historical convention has the implication that the Earth has its geomagnetic south pole in the geographic north hemisphere. – dmckee --- ex-moderator kitten Jun 23 '19 at 15:06

To answer that you need to know that in a classical mechanic view elementary quantities of magnetic field are generated by small loops of current call magnetic dipoles. Macroscopic magnet are only an assembly of elementary magnetic dipoles in macroscopic dipole. Although the magnetic field generated by permanent magnet is purely quantum physics (so moving charges are not define) the analogy remain acceptable. The direction of the magnetic field is only define by the direction of current in the loop (clockwise or anti-clockwise), by reversing the current you invert poles. So north pole is define as the pole above a loop of "clockwise" current (an below anti-clockwise). The field goes out the north pole of a magnet and goes in the south pole of the magnet. This property come from link between current and magnetic field : Biot-savart law (or Ampere-Maxwell equation) which describe the magnetic field as the vector product of the current and the vector joining the elementary current element and the point as which the field is being compute.

Like for the electrostatic where positive (or negative) charged macroscopic object mean absence (or present) of electron, a macroscopic magnetic object indicate present of extra dipoles from on kind (clockwise or anti-clokwise). north and south pole will be define by those in excess.

edit: "of course" contrary to the charge where it exist two kind of charges (positive and negative) the two kind of dipoles are the same but flip upside down. The clockwise or anti-clockwise type of a dipole is not an intrinsic property but can be "easily" change. A "strong" magnetic field can flip the internal elementary dipole of a permanent magnet and consequently reverse the pole of the magnet.

You are right up to a point about the charges on an atom,but you don't seem to understand what charge itself is. Charge is the source of a force vaguely similar to gravity, but trillions of times stronger. This force is called the electromagnetic force. Few people realise how powerful it is. In particles which can be observed in isolation, it is always the same as the charge on the electron or multiples thereof, and may be positive or negative. An alpha particle has a double charge because it contains two protons, which each have the same charge as an electron but of opposite sign.

To return to magnets, just as for every positively charged particle there must be a negatively charged one, for every south pole there must be a north pole. You can tell which is the north pole of your magnet by putting it against the north pole of another magnet. If it repels, you have put two north poles together, but if it attracts, you have put your south pole against the north pole of the other. It is the electromagnetic force emanating from the particles within the magnet which creates this repulsion or attraction. If it doesn't seem to be trillions of times more powerful than gravity, that's because your magnet contains equal numbers of negatively charged particles which cancel out the effect of the positive charges.

• Nobody knows what charge "is". – my2cts Jun 23 '19 at 10:09

The Maxwell equation $$\vec \nabla \cdot \vec B=0$$ prohibits the existence of magnetic monopoles. We know that Maxwell's theory is the basis of a correct description of nature. Even if this equation were not always true, it would still be true for the magnetism that we know. Magnetic monopoles would give new physics.

• I don't think it answers the question at all. OP knows there are two poles. The question is why is the North Pole considered a magnetic north pole. – Eric Duminil Jun 23 '19 at 17:24
• @EricDuminil The OP asks what the poles are made of. – my2cts Jun 23 '19 at 20:07
• I might be missing something, but I see no indication that it is the case. – Eric Duminil Jun 24 '19 at 8:18
• @EricDuminil "Like in case of charges, positive and negative charge on an atom means absence and presence of extra electrons respectively. So my question is what aspect exactly makes a pole of magnet north or south? Is it absence or presence of something?" – my2cts Jun 24 '19 at 9:15