Basic physics question

my understanding is that people at first were unaware of the charge of electrons. a convention of current moving from + to - was established, and never really changed, since it doesnt matter for everyday problems really.

Current travels from + to -.

In what direction the actual particles carrying the charge travel depends on their charge: negatively charged particles (like electrons) move from - to +, positively charged particles (like H+ ions) move from + to -.

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Original post by Trap Current travels from + to -. In what direction the actual particles carrying the charge travel depends on their charge: negatively charged particles (like electrons) move from - to +, positively charged particles (like H+ ions) move from + to -.

So if I understand it right (I doubt it), it depends on the kind of current. You call "start" + and the "end" -, no matter what. Electric current also travels from + to -, but it's actually from a negative pole to a positive pole, they are just marked - and + respectively?

EDIT: Just checked it out on Wikipedia and it seems that it depends on the material used to transport the current, for instance in solid metals the electrons is the current, but in other materials like ice it's actually positivly charged current (I don't know what it's though, I doubt it's the protons, so it might just be ions like H⁺). I'm still confused whether the start of the current is always called +, or it's called whatever it actually is.

[Edited by - CTar on June 11, 2006 1:16:22 PM]

Generally, positive charge carriers go from + to - and negative charge carriers go from - to + . With metals you have negative charge carriers only, with electrolytes you have positive and negative ions, in spark you have positive ions, negative ions, and free electrons.

Note that the choice which charge is "positive" was entirely arbitrary historical thing (it coulda have happened that electrons would be said to be "positive"), but choice of 'direction of current' is linked to choice of "positive" - it is the direction where "positive" charge goes (always).

That makes sense, example: when you have something charged positively and something else negatively, if you connect these things and let current flow, the charge(quantity) of negatively charged thing will increase, and charge of positively charged thing will decrease. That is, the quantity of "charge" has transferred from positive to negative. Regardleess of what kind of particles transferred it.

It is same as direction of electric field (charges don't move by themselves, them is moved by electric field)

[Edited by - Dmytry on June 11, 2006 2:43:05 PM]

In an electric circuit so called conventional current goes from + to -, however what's actually happening is the negatively charged electrons move from - to +. The reason coventional current is mentioned in the context of electrical circuits is a historical quirk as Eelco said.

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I'm still confused whether the start of the current is always called +, or it's called whatever it actually is.

The + pole is always the + pole. It doesn't depend upon where the charged particles originate from.

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Original post by CTar EDIT: Just checked it out on Wikipedia and it seems that it depends on the material used to transport the current, for instance in solid metals the electrons is the current, but in other materials like ice it's actually positivly charged current (I don't know what it's though, I doubt it's the protons, so it might just be ions like H+). I'm still confused whether the start of the current is always called +, or it's called whatever it actually is.

It's neither protons nor H⁺ ions. You're probably thinking of semiconductor materials and "holes." The idea is that there are receptor sites (lack of bonds) in a crystal lattice and electrons will move into these sites. Each time this occurs, a "hole" is left behind. This lack of an electron is effectively a net positive charge. As the electrons move in one direction, the holes appear to be moving in the opposite direction.

Imagine billiard balls:

OOO OO

Moving one at a time to the right, this happens:

OO OOO
O OOOO
OOOOO

The gap appears to be moving to the left but the balls are actually being moved to the right.

In solid materials it is almost exclusively negative charge (electrons) that "move".

But consider, the reason conductive materials conduct (in solids, anyway) is because the crystalline structure leaves free electrons or holes where electrons can go. In these cases, if the atoms only had enough electrons to perfectly bind with adjacent atoms, then it would have net positive or negative charge which causes these free electrons or "holes" to form.

In practice, current can always be thought of as positive charges flowing from + to -. You would have to be doing some specialized physics in order for it to matter.

In fact, it is even considered electrical engineering standard to have current flowing positive to negative. Only physicists trying to be completely accurate, and engineers in the navy(!) have current flowing from negative to positive.

Besides, the sort of idea that electrons leave the negative terminal of the battery and travel to the positive terminal is wrong anyway. Electrons in a conductor don't travel very fast at all. A more accurate picture is the billiard balls as shown above.