This is a bad habit. Generally the direction current is all that matters, and not the polarity of the charge carriers. The instances where the polarity of the charge carriers is important are very few and far between (e.g. the Hall effect). Unless you are working with one of those you will be better off simply thinking about the direction of the current.
This is not generally true. There are circumstances where the charge carriers are positive. E.g. proton beams. There are even cases where the charge carriers are both positive and negative. E.g. electrolytes. In particular, when you have both positive and negative charge carriers trying to think in terms of both ion flows will lead to nothing but confusion.
This is wrong. Current can easily be negative. As ZapperZ mentioned above, the quantity that is actually of interest for physics is not current, but current density, which is a vector. When you go from current density to current you have to specify a surface and a surface normal, at least implicitly. Once you do so, a current going one way across the surface is positive and a current going the other way across the surface is negative.
You can have a current of both and charges do move.
They either have to go from north to south or from south to north. We just picked a convention and used it. It is just a convention, use it consistently and you will get the right answer for any measurement you choose.
This is not the bad manner but just the healthy contradiction. How can charges move ? In proton accelerators we move a proton which is just a subatomic particle having +1 charge.
So the particle is moving and not the charges I think.
... I was hoping you'd link the magnetic field from electric currents with the magnetic field from a bar magnet. How would does the arrangement of electrons relate to an electric current?
In the planetary model of the atom - electrons orbit the nucleus in a circle[*]. An electron moving in a circle is an electric current in a loop (see pic below) - so we would expect atoms to have a magnetic field the same way a current loop does. In a solid object, the atom's magnetic fields are randomly arranged, so they mostly cancel each other out and what's left is too small to notice. In a permanent magnet, enough atomic magnetic fields are oriented the same way to be noticed.
I kinda like this example because it illustrates how connected everything gets when you look carefully.
Note: we often use magnitudes of vectors in calculations - for convenience. eg. gravitational force and acceleration are usually quoted as scalars even though they are vectors ... the direction is taken from context.
When we talk about current in a DC electric circuit, the direction of the current almost always makes no difference to the results of our calculations while making the actual math harder so we leave it off. However, if you look at circuit analysis - like Kirkoffs Laws - you will see current is always drawn as an arrow (vector). In AC circuits, the current and voltage are described as a rotating vector called a phasor.
Because it can make a difference, we need to remember this and adjust what we do when it becomes important. Usually we can get the direction from the context when this happens. In the equation you use an an example, the only part of the current that is affected is the magnitude. The direction is implied.
Basically, we don't like to do more math than we have to.
-- -- stolen from: PHYSICS 51 notes San Jose University.
The [itex]\bf \mu[/itex] is the direction of the north pole and is called the "magnetic moment". The [itex]\bf L[/itex] is the moment of inertia of the electron.
[*] The actual situation is more subtle than that - but atoms still have their own magnetic fields - called "magnetic moments" - which come from the symmetries in the electrons.
Hmm little sophisticated to grasp but its a bit satisfying.
Here was my complete answer (quoted) :
The answer is but the Earth's magnetic field. It flows from south pole to the north pole. When it links itself (magnetic flux) with a permanent magnet , it induces opposite poles in permanent magnet in which magnetic lines of forces flow from north pole to south pole. This is due to the process mutual magnetic induction.
Now the question arises that if we keep an iron bar will it behave as a magnet ? No ! We must convert it to a magnet : Single touch method , divided touch method , double touch method or electrical method. If we follow either of methods electrons come in pairs in straight lines having net electrostatic force. This is Ewing's molecular theory of magnetism.
e- e- e- e- e- e- e-
e- e- e- e- e- e- e- --> Like this in a permanent bar magnet.
Like this in normal iron bar :
e- e- e-
Its correct , according to you ? Right ? Yes I know that in magnets electrons form straight line giving rise to net force attraction. In iron bars , the electrons in random pattern mutually cancel each others force of attraction , giving rise to zero net force. I could even more elaborate but my hand would ache very badly so I thought it might me better to be brief here.
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