Science Questions

Is north really north?

Tue, 24th Dec 2013

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Stephen Hayes asked:

I'm an applied science student at Open University Australia, and I was wondering why magnetic north is not called south as a positive will repel another positive. When a needle is magnetised, it is repelled from the south and is attracted to the north. Is the world really upside down and is Australia really the land down under?


Many thanks


Stephen Hayes


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According to Wikipedia:
A magnet or compass needle's "north" pole is defined as the one which is attracted to the North magnetic pole of the Earth. Since opposite poles attract ("north" to "south") the North magnetic pole of the Earth is actually the south pole of the Earth's magnetic field. The compass needle's north pole is always marked in some way: with a distinctive color, luminous paint, or an arrowhead.

Defining north and south for an electromagnet can be even more confusing.
According to Wikipedia:

The direction of the magnetic field through a coil of wire can be found from a form of the right-hand rule. If the fingers of the right hand are curled around the coil in the direction of current flow (conventional current, flow of positive charge) through the windings, the thumb points in the direction of the field inside the coil. The side of the magnet that the field lines emerge from is defined to be the north pole.

We now know that current in a wire is a movement of negatively charged electrons. Had we known that sooner, the electron's charge would have been defined as positive.

On a related note: I vehemently disagree with the way we define north and south galactic poles. The sensible definition would be the right hand rule; the north pole of ANY rotating body should be the way the thumb of the right hand points when the fingers point in the direction of rotation. By that rule, the Milky Way's Galactic North Pole would be in Earth's southern hemisphere. What dummy decided that our Solar system must dictate which way is north for all rotating bodies in the universe? The north poles of all rotating bodies are now determined by their orientation relative to our solar system's rotation. What about those whose axes are perpendicular to that of our solar system? I guest their north poles are defined by a coin flip.

Wikipedia: Galactic coordinate system Phractality, Sat, 14th Dec 2013

Because the North geographic pole was given that name before the discovery of magnetism. It was only later that it was realized that the North geographic pole was a south magnetic pole. But by that time the names were too well known and there's insufficient reason to change them. Pmb, Sat, 14th Dec 2013

There is another wrinkle: The polarity of Earth's magnetic field switches occasionally (on average about twice per million years).

see: chiralSPO, Sun, 15th Dec 2013

When Earth's magnetic field reverses, will we change the definition of "magnetic north pole"? Will the north pole of a compass needle still be the one that points roughly toward geographic north? Phractality, Sun, 15th Dec 2013

I think it will be easier to keep the current labels on the compass needle - if anyone still has a compass with a physical needle.

Some suggest that the Earth's dipole field will not suddenly switch off, but will pass through a quadrupole phase, where there is more than one North Pole.

During this transition, your compass will point to the nearest North Pole, which is likely to be far from the axis of rotation. Unless you are a airline pilot, it will be easier It will be easier to keep calling it magnetic North, rather than the South-American Pole.

I expect by then we will have Apps that determine your location from GPS, lookup this month's magnetic map which includes both direction & inclination of the magnetic field, and point you towards the North rotational axis (True North)... evan_au, Mon, 16th Dec 2013

No. The definition of magnetic north wont change, only its direction/location will change. The magnetic north will then become the geographic north (or at least close to it).
Pmb, Mon, 16th Dec 2013

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