Is the Direction of Magnetic Fields Truly Conventional?

[pgirl1729]

TL;DR Summary

Based on what theory do they mark the magnetic field from north to south?

In many books, the direction of the magnetic field is mentioned as north to south. It says they have marked it because the north pole of the compass faces to south. But why can't we say the direction is the opposite of it as the south also attracts to north? When I browsed answers, most replies were saying it was conventional. Then exactly what could be the direction of the magnetic field? Actually, is there a direction at all? Can it be call a vector quantity

 

[Ibix]

But why can't we say the direction is the opposite of it as the south also attracts to north?

You can. But then you have to remind everyone you communicate with that you're using the opposite sign convention to everyone else. And you have to work out where to put the minus signs in the maths because you've defined one vector as minus the usual definition.

Actually, is there a direction at all? Can it be call a vector quantity

Yes, the magnetic field is a vector field, yes it has a direction.

 

[pgirl1729]

How would you prove it has a direction? In displacement, the direction can be determined by seeing the motion.

 

[Ibix]

How would one prove it has a direction?

Predict an effect based on assuming it's a vector (e.g., that electronics work) then test it (they do).

 

[Vanadium 50]

The magnetic field exerts a force on a moving charge. That force obviously has a direction.

 

[pgirl1729]

Predict an effect based on assuming it's a vector (e.g., that electronics work) then test it (they do).

That helped. Thank you!

 

[Dale]

TL;DR Summary: Based on what theory do they mark the magnetic field from north to south?

Then exactly what could be the direction of the magnetic field? Actually, is there a direction at all? Can it be call a vector quantity

As @Ibix said, the direction is a matter of convention. We have written all of our formulas with the right hand rule convention such that the field vectors point out of a north pole and into a south pole. We could instead use a left hand rule and the field vectors would point out of a south pole and into a north pole.

Technically, objects that behave this way are not actually vectors. Instead they are called pseudo-vectors. In 3 dimensions they behave a lot like actual vectors, except that under certain transformations of the coordinates they get flipped.