Positive and Negative Current

[Stiganator]

This is a quick one,

Current by definition is the flow of electrons and they have an negative charge.

How can you have positive current?

 

[PottedMeat]

Flow of holes ( opposite of negative current )

 

[BrownTown]

In science negative just means "opposite" most of the time, its just a RELATIVE term to a predefined value. In the sense of current a negative current simply means that electrons are flowing opposite of the arbitrarily set direction. Also FWIW positive current means electrons are AGAINST the direction of the current. So if you have a current of 1A going into a device what that really means is that 1 coulomb of electrons are LEAVING the device per second, not entering. As for the flowing of holes, they are an imaginary construct defined as a positive charge carrier, but they do don't exist in reality as such. A "hole" is simply an atom at a lattice site which does not have as many electrons as it should, when holes are flowing one way what that really means is that electrons are flowing the other.

 

[futuristicmonkey]

The reason for this old, sometimes annoying concept is when they assembled the first battery they assumed current was flowing out of the top of the battery. No joke.

-ben

 

[Throckmorton]

So electricity flows out of the negative end of the battery right? Does that mean that current flows from the ground wire on a powersupply to the positive red or yellow wire?

 

[BrownTown]

Originally posted by: Throckmorton
So electricity flows out of the negative end of the battery right? Does that mean that current flows from the ground wire on a powersupply to the positive red or yellow wire?

no, "electricity" flows out of the positive end, but ELECTRONS flow out of the negative end, so yes if you were following an electron around a circuit it flows out of the "Gnd" wire on the power supply through the circuit and back in the +5V (or whatever) wire.

 

[Mark R]

Current flows from the positive to the negative end of a battery or power supply. This is how it is written, described and measured. So, for example, if you are calculating the magnetic field caused by a current - the direction of the current is in the positive to negative direction. In other words, in your example, the current flows from the red (or yellow) wire through the load, and into the black.

If you go beyond the concept of bulk flow in the wire, and look at how the actual current is carried, then things become more complicated. In metal, the electrical current is carried by electrons. Electrons have a negative charge, and so the physical direction that the electrons move in must be opposite to the direction of the current flow.

Electrical current isn't always carried by electrons. If you pass an electrical current through a substance like molten salt (sodium chloride), then half of the current is carried by positively charged sodium ions. These flow in the conventional current direction - from positive to negative - and congregate at the negative electrode where they pick up electrons from the electrode and form sodium metal (and this is how metallic sodium is produced). The negative chloride ions carry the other half of the current, and flow in the reverse direction (same as electrons) from negative to positive (where they dispose of their excess electrons to the electrode and form chlorine gas).

 

[RossGr]

In an ionized solution, such as salt water, positive ions carry current as well as negitive. Electrons are the current carriers in metalic conductors, but not everywhere in everything.

 

[veri745]

Originally posted by: BrownTown
As for the flowing of holes, they are an imaginary construct defined as a positive charge carrier, but they do don't exist in reality as such. A "hole" is simply an atom at a lattice site which does not have as many electrons as it should, when holes are flowing one way what that really means is that electrons are flowing the other.

This isn't quite true. It's true that holes are a lattice sites with vacant electrons, but holes are not a purely 'imaginary construct'. Particularly in semiconductor device physics, a hole has a different mass than an electron, and therefore is affected by electric fields differently. Holes simply behave like a separate particle from electrons, and it's not just a mirror image.

 

[BrownTown]

Originally posted by: veri745

Originally posted by: BrownTown
As for the flowing of holes, they are an imaginary construct defined as a positive charge carrier, but they do don't exist in reality as such. A "hole" is simply an atom at a lattice site which does not have as many electrons as it should, when holes are flowing one way what that really means is that electrons are flowing the other.

This isn't quite true. It's true that holes are a lattice sites with vacant electrons, but holes are not a purely 'imaginary construct'. Particularly in semiconductor device physics, a hole has a different mass than an electron, and therefore is affected by electric fields differently. Holes simply behave like a separate particle from electrons, and it's not just a mirror image.

Yes, thats true, but there is no particle called a "hole", there is certainly a different set of parameters that apply to holes though which is why it is helpful to think of them as a separate entity.

EDIT: just for those who want more info I'll link the wiki page.

 

[WildHorse]

Current flows from the positive to the negative end of a battery -Mark R

Are you sure?
That's exactly backward from what I've always thought.

I've always understood that at one pole the atoms with "more losely bound" electrons have a negative charge, and atoms at the other pole that will accept those free electrons into valence shell vacancies have a positive charge.

Consequently, electrons flow from the negative end having "surplus" electrons, and toward the positive end having vacancies to accept electrons.

It will be good for me to nail down a correct understanding, so I look forward to further clarifications provided in this thread.

 

[esun]

Scott, you're confusing the flow of electrical current with the flow of electrons. By definition, electrical current is the flow of positive charge. That means if I have electrons flowing one way (in this example, from the negative battery terminal to the positive battery terminal), then I have electrical current flowing the other way. It's just convention.

Since no one's linked it yet, here's the Wikipedia article on electrical current: http://en.wikipedia.org/wiki/Electric_current

 

[WildHorse]

esun,

Thank you!

I see you're in Trabuco Canyon.

Once upon a back in college when I had no car, I hitchhiked to that Vedanta monastery there and spent hours talking with the monks. They have another place close to my home (Santa Barbara area) I visited too. Interesting. I really love exploring ideas and other ways of thinking like that.

I guess that Trabuco Canyon Monastery was started up as something else, maybe by Aldous Huxley? They said it was a hang out for literary elite people and movie stars beforeit became a monastery. Do you visit it?

 

[esun]

Can't say I've ever even heard of it.

 

[DrPizza]

A little late with this post, but the flow of electrons doesn't "begin" at one end of a battery and "end" at the other end. It's a continous path, including through the battery/power supply.