Direction of current flow

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teufelhounden91

teufelhounden91

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Every book on electrical theory that I've read states the current flows from negative to positive in a dc circuit.

Why then are the battery terminals in a car hooked up with black (neg) to the chassis/ground and the red (pos) to the loads. In automotive the current, as I understand it, leaves the positive terminal, flows through the loads, to the chassis, then back to the positive terminal.

Isn't this backwards from how were taught?


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electrons flow from neg (thats where they all hang out, they are all amp'd up, etc) to the pos (where the party's at).

some look at the holes that move, others look at the electrons that move.
they have to cross a load from one terminal to the other, no way around that.

the only way to show it is to look at the magnetic field lines around one of the batt cables. they have a direction perpendicular to the amps flow, but there are two directions perpendicular to amps flow separated by 180 degrees, but the right-hand rule can show you, but right-hand is if you follow amps by moving holes, left-hand rule if you follow the moving electrons, either of them properly show the magnetic direction.
 
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teufelhounden91 said:
Every book on electrical theory that I've read states the current flows from negative to positive in a dc circuit.

Why then are the battery terminals in a car hooked up with black (neg) to the chassis/ground and the red (pos) to the loads. In automotive the current, as I understand it, leaves the positive terminal, flows through the loads, to the chassis, then back to the positive terminal.

Isn't this backwards from how were taught?


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Click to expand...

Which one is grounded won't make any difference in which direction current flows, just which terminal has a ground reference is all.

Some older vehicles (I think) and older machines (like tractors) did ground the positive battery terminal.

One could build a multiwire DC source (simple two cells in a series with midpoint made accessible for circuit usage is an example) and ground the midpoint and you still have positive to one side and negative to the other side, and a ground reference that is positive to one side and negative to the other.
 
kwired said:
Which one is grounded won't make any difference in which direction current flows, just which terminal has a ground reference is all.
Click to expand...

well, to be fair, if we look at the frame rail and put an arrow on it which way amps is flowing (amps + direction = vector) the arrow will face one way, then when you swap everything around the arrow will face the other way.

but always, no exceptions, electrons move from neg to pos, and holes move from pos to neg.
 
Electrons flow from negative to positive. In some semi-conductors, "holes" flow from positive to negative.

You can blame Ben. Franklin for putting the + on the "wrong" end.

For a physicist, current (sometimes called "conventional current") flows from + to -. For most everyone else, current (electrons) flow from negative to positive.
 
teufelhounden91 said:
Every book on electrical theory that I've read states the current flows from negative to positive in a dc circuit.

Why then are the battery terminals in a car hooked up with black (neg) to the chassis/ground and the red (pos) to the loads. In automotive the current, as I understand it, leaves the positive terminal, flows through the loads, to the chassis, then back to the positive terminal. ...
Click to expand...

Blame Ben Franklin (or someone else of his ilk). He picked charge carriers (electrons) as negative. Electrical Theory text books use electrons as the charge carriers so "current flow" is from the Negative to the Positive.

Engineering texts tend to use "conventional". The charge carrier is the hole in the atom where the electron moved from. So while the electron is moving one direction (negative to positive) the "holes' left behind when the electron moves, is moving the other direction, positive to negative. Just means the engineers get to do their math models with a few less minus signs.

And it really doesn't matter. Just have to pick one and stay consistent. Math works out the same.

If Ole Ben had picked electrons as positive, we would have painted the other post on the battery red and swaped the connections.

ice
 
Here is a post from another thread on this topic:

"Let's temporarily ignore all notions of electron drift and pretend that individual electrons do race all the way around the circuit. When an electron moves from one location to another, it leaves behind an empty spot, a hole, that at that moment has a net positive charge. When another electron moves into that spot, the hole is filled, but another hole is created in the location that the second electron vacated. As viewed from the outside world, the hole appears to have moved in the opposite direction that the electron really did move. You can think of this as negative charge moving in one direction, or as positive charge moving in the other direction. This is the essence of the conventional current approach."

That is post #19 by Charlie b in this thread: http://forums.mikeholt.com/showthread.php?t=164038&page=2&highlight=which+way+does+current+flow?
 
151106-1948 EST

Direction of current flow is based on a definition.

In an external circuit the two different standard definitions are:
Note that the current flow direction is in the opposite direction within an energy source (the internal citrcuit) as compare to the external circuit.

Conventional flow --- current flows from positive to negative.
Electron flow --- current flows from negative to positive.

For any circuit analysis to be successful you must stick with one definition or the other. I believe all US engineering schools will use "conventional flow" as the definition of current flow for circuit analysis.

Direction of current flow has nothing to do with where someting is earthed or connected to a chassis or cabinet.

If I analyze a circuit that contains an electron tube, then the direction of current flow is from the plate to the cathode. Physically inside the tube current is flowing via electrons from the cathode to the plate.

.
 
FionaZuppa said:
electrons flow from neg (thats where they all hang out, they are all amp'd up, etc) to the pos (where the party's at).

some look at the holes that move, others look at the electrons that move.
they have to cross a load from one terminal to the other, no way around that.

the only way to show it is to look at the magnetic field lines around one of the batt cables. they have a direction perpendicular to the amps flow, but there are two directions perpendicular to amps flow separated by 180 degrees, but the right-hand rule can show you, but right-hand is if you follow amps by moving holes, left-hand rule if you follow the moving electrons, either of them properly show the magnetic direction.
Click to expand...

Back to basics, should have thought of that. Thanks kwired


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mgookin said:
Here is a post from another thread on this topic:

"Let's temporarily ignore all notions of electron drift and pretend that individual electrons do race all the way around the circuit. When an electron moves from one location to another, it leaves behind an empty spot, a hole, that at that moment has a net positive charge. When another electron moves into that spot, the hole is filled, but another hole is created in the location that the second electron vacated. As viewed from the outside world, the hole appears to have moved in the opposite direction that the electron really did move. You can think of this as negative charge moving in one direction, or as positive charge moving in the other direction. This is the essence of the conventional current approach."

That is post #19 by Charlie b in this thread: http://forums.mikeholt.com/showthread.php?t=164038&page=2&highlight=which+way+does+current+flow?
Click to expand...

Thank you, never through the holes were important other than that they accept electrons. That helped clear this up for me.


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gar said:
151106-1948 EST

Direction of current flow is based on a definition.

In an external circuit the two different standard definitions are:
Note that the current flow direction is in the opposite direction within an energy source (the internal citrcuit) as compare to the external circuit.

Conventional flow --- current flows from positive to negative.
Electron flow --- current flows from negative to positive.

For any circuit analysis to be successful you must stick with one definition or the other. I believe all US engineering schools will use "conventional flow" as the definition of current flow for circuit analysis.

Direction of current flow has nothing to do with where someting is earthed or connected to a chassis or cabinet.

If I analyze a circuit that contains an electron tube, then the direction of current flow is from the plate to the cathode. Physically inside the tube current is flowing via electrons from the cathode to the plate.

.
Click to expand...

Im not an engineer so I apologize but this confused me a bit more. Are you saying that in a wire the electron movement is from negative to positive. But the magnetic field direction is opposing that (pos to neg)?


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151107-0959 EST

teufelhounden91:

Forget about any physical relationship of particles moving and direction of current flow.

When a circuit is drawn on paper and an arrow is placed on the paper to indicate a direction of current flow, then some convention has to be established that relates current and voltage for analysis purposes.

For the conventional current flow definition.

Consider a battery, wires, resistors, and some other batteries. By definition "conventional current" flow says that current flow from the + battery terminal of a first battery to a resistor connected across said first battery is positive. This imaginary current (there is no actual current flow in the pencil line on the paper) is from the first battery + terminal to the resistor end connected to the + battery terminal.

Remove the resistor end connected to the - terminal of said first battery and connect this to the + terminal of a second battery that has a greater voltage than the first battery. Connect the negative terminals of the two batteries. Now current flow from the first battery + terminal is negative (current is flowing into the first battery). But positive current is flowing from the + terminal of the second battery toward the + terminal of the first battery.

This still may not help you. Ask more questions.

.
 
Negative to positive fur shure

Negative to positive fur shure

So the way I was taught, look to the atomic level. The "party" is at the center, where the protons, or positively charged particles, and the neutrons, or neutral particles, of which there is an equal proportion, are hanging together having a grand time! the electrons, or negatively charged particles, are kinda circling around, trying to get invited in for a drink or two (not really, but whatever) 'cause they are oh so attracted to the protons! Suddenly a switch is closed allowing current flow, and here comes a free electron (not attached to anything, but negatively charged nonetheless) and wants to crash the party. He (or she in the brave new world of political correctness)
runs full bast, crashing into the valence ring. Since the copper atom can only have 7 (seven) electrons in it's valence ring, another electron is knocked loose, becoming a free electron, and so on and so forth, ad infinitum, a chain reaction, if you will.
And hence the the electron theory is born, yes? electron flow is, in fact, from negative to positive (electrons, after all, being negatively charged, being attracted to the protons, which are, of course, positive).
Whew, glad I still have my Delmar's for reference lol!
 
teufelhounden91 said:
Every book on electrical theory that I've read states the current flows from negative to positive in a dc circuit.

Why then are the battery terminals in a car hooked up with black (neg) to the chassis/ground and the red (pos) to the loads. In automotive the current, as I understand it, leaves the positive terminal, flows through the loads, to the chassis, then back to the positive terminal.

Isn't this backwards from how were taught?


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Click to expand...

Cars used to be positive ground. I have heard a couple reasons for changing. One is that supposedly negative grounded cars protect the copper wiring which is usually positive from corrosion.

Another was to make the center electrode of the spark plugs positive. I was told that made the plugs last longer.

Google has a few more reasons. Perhaps the real reason is lost to history.
 
Barbqranch said:
Electrons flow from negative to positive. In some semi-conductors, "holes" flow from positive to negative.

You can blame Ben. Franklin for putting the + on the "wrong" end.

For a physicist, current (sometimes called "conventional current") flows from + to -. For most everyone else, current (electrons) flow from negative to positive.
Click to expand...

This confuses the heck out of me :lol::dunce: To this day I still have trouble understanding it. Does anything flow in conventional current from positive to negative?
 
gar said:
151106-1948 EST

Direction of current flow is based on a definition.

In an external circuit the two different standard definitions are:
Note that the current flow direction is in the opposite direction within an energy source (the internal citrcuit) as compare to the external circuit.

Conventional flow --- current flows from positive to negative.
Electron flow --- current flows from negative to positive.

For any circuit analysis to be successful you must stick with one definition or the other. I believe all US engineering schools will use "conventional flow" as the definition of current flow for circuit analysis.

Direction of current flow has nothing to do with where someting is earthed or connected to a chassis or cabinet.

If I analyze a circuit that contains an electron tube, then the direction of current flow is from the plate to the cathode. Physically inside the tube current is flowing via electrons from the cathode to the plate.

.
Click to expand...

Arent in theory all semiconductors graphically incorrect?
 
Johnnybob said:
So the way I was taught, look to the atomic level. The "party" is at the center, where the protons, or positively charged particles, and the neutrons, or neutral particles, of which there is an equal proportion, are hanging together having a grand time!
Click to expand...
There is an equal number of protons and electrons in an atom but the number of neutrons varies per isotopic differences. For example, Carbon 12 has 6 protons, 6 electrons, and 6 neutrons, but Carbon 14 has 6 protons, 6 electrons, and 8 neutrons.
 
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151107-1303 EST

mbrooke:

Direction of current flow for analysis purposes is determined by a definition and has nothing to do with any physical particle movement

.
 
Ah, yes, and I obviously haven't spent enough time with my Delmar's lately, for some reason I erroneously thought that copper, while being a fairly good conductor, has 7 valence electrons, when in reality it only has 1? anyway,I guess i should stay out of these conversation's but then I wouldn't keep learning. That doesn't change my belief that electron flow is in fact from negative to positive!:D
 
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