In what direction does electricity flow? Beyond confused

[mbrooke]

Ok, yes I am the same person, feeling ok, and not a DIY:lol::lol: More like this>:dunce:


I have always been taught that electricity flows from negative to positive. However, I see so many books, especially old ones claiming its from positive to negative. In fact, its not just a few, but hundreds over the years I have encountered. Even detailed graphics. In fact Id say its close to 1/3 to half the books. :blink:

To make matters worse, I find conflicting graphics all the time in which direction power flows in a diode. Some point through the arrow positive to negative which makes sense, but so many show negative to positive going opposite the arrow.


Here are some from a Google search, the first 10 automatically conflict one another, even the vacuum tube shows electrons boiling off the filament, yet an arrow goes toward the cold plate labelled current?

I am beyond confused.:?:?:?

 

[Besoeker]

It's a matter of convention.
The flow of electrons, or drift is a better word, is from negative to positive in a DC circuit. For individual electrons it isn't much (1.6*10^-19 C) but there are a lot of them in most conductors.
For AC circuits, the electrons just wiggle back and forth a bit. A very little bit.

 

[GoldDigger]

Ben Franklin had to choose a direction to be positive for current flow. Not knowing about electrons, he had a 50% chance of guessing right. He missed.
Positive current flow (from + to -) is the direction that makes all of the equations work. That is the sum total of its metaphysical significance.

 

[mbrooke]

Ben Franklin had to choose a direction to be positive for current flow. Not knowing about electrons, he had a 50% chance of guessing right. He missed.
Positive current flow (from + to -) is the direction that makes all of the equations work. That is the sum total of its metaphysical significance.

So it was believed it went from positive to negative? Then it changed?

 

[GoldDigger]

So it was believed it went from positive to negative? Then it changed?

At the time the choice was made it was not known whether the mobile charge carriers were positively or negatively charged. So the "current" that flowed was entirely arbitrary.
In electrolytes and some other places the moving charge carriers are positive ions. But that has no effect on the designation of current flow either.

 

[mbrooke]

At the time the choice was made it was not known whether the mobile charge carriers were positively or negatively charged. So the "current" that flowed was entirely arbitrary.
In electrolytes and some other places the moving charge carriers are positive ions. But that has no effect on the designation of current flow either.

Id guess that notion also led to diodes getting an arrow positive to neg?

 

[GoldDigger]

Id guess that notion also led to diodes getting an arrow positive to neg?

Yup.

 

[gar]

140823-1439 EDT

mbrooke:

As Besoeker said it is by convention, meaning by definition.

Direction of current flow was originally defined as from + to - in the external circuit before knowledge of the existence of charged particles, for example the electron. The external circuit is that outside of the energy source. Inside an energy source the current flow is in the opposite direction of that on the outside when referenced to the + and - terminals.

For circuit analysis it is necessary to have a fixed definition for the direction of current flow. I believe all engineering schools world wide use "conventional current flow" (from + to -) as their standard for circuit analysis, even for vacuum tubes. This is in contrast to electron flow which is from - to +.

What is actually moving in any device, material, or media depends upon its composition.

In an electron tube current actually flows by a movement of electrons from the filament or cathode to another more positive electrode, such as the plate. These electrons actually move over this path very fast, but not so fast that electron tubes don't start to have a problem around 1000 MHz. But still for analysis one uses "conventional current flow".

.

 

[Barbqranch]

Same is true in the physics classes I took, it was referred to as "conventional current". Always plus to minus. Even though we all knew in most cases it was electron flow ("electron current") going the opposite.

 

[mbrooke]

140823-1439 EDT

mbrooke:

As Besoeker said it is by convention, meaning by definition.

Direction of current flow was originally defined as from + to - in the external circuit before knowledge of the existence of charged particles, for example the electron. The external circuit is that outside of the energy source. Inside an energy source the current flow is in the opposite direction of that on the outside when referenced to the + and - terminals.

For circuit analysis it is necessary to have a fixed definition for the direction of current flow. I believe all engineering schools world wide use "conventional current flow" (from + to -) as their standard for circuit analysis, even for vacuum tubes. This is in contrast to electron flow which is from - to +.

What is actually moving in any device, material, or media depends upon its composition.

In an electron tube current actually flows by a movement of electrons from the filament or cathode to another more positive electrode, such as the plate. These electrons actually move over this path very fast, but not so fast that electron tubes don't start to have a problem around 1000 MHz. But still for analysis one uses "conventional current flow".

.

Ok its getting clearer. But still very confusing when colleagues have different knowledge of the same. Seems like some where taught one way others another.


I can get the regular "classical" analysis perhaps holding true for diodes, but not for vaccum tubes.


My understanding, and correct me if Im wrong, is that the filament in simple vacuum tube diodes is considered "negative" and always has been, while the cold plate is the positive. How could it be explained in classical terms that a cold plate can emit electrons, or just pass electricity before electrons were known about? Or was the cold plate considered the negative when plus to minus theory existed? :?

 

[GoldDigger]

The tube diode is just like the semiconductor diode in that the current can flow only in one direction, namely from the plate to the filament/cathode.
The fact that the current flows from plate to cathode while the electrons flow in the opposite direction, is just another instance of conventional current formalism.

 

[gar]

140823-2345 EDT

mbrooke:

By definition the direction of current flow in a "conventional current" analysis is that current flows from the most positive terminal of a load device to the more negative terminal. This is totally independent of what is the actual mechanism of current flow in the load device.

In a vacuum tube diode there are electrons boiling off of the hot filament or cathode. This is called a space charge. If an electrode is inserted into this tube (the plate in a vacuum tube or a wire in the Edison Effect experiment) and this electrode is made more positive than the cathode, then a conventional current flows from the positive plate to the more negative cathode. But the actual mechanism of current flow was electrons being accelerated to the plate by its positive potential.

Make the diode plate more negative than the cathode and the electrons are repelled and no current flows.

To avoid confusion disregard the mechanism of current flow and only concentrate on the definition of "conventional current" flow.

.

 

[Curious nerd]

Or was the cold plate considered the negative when plus to minus theory existed? :?

"Positive" got defined long, long, before vacuum tubes.

 

[mbrooke]

The tube diode is just like the semiconductor diode in that the current can flow only in one direction, namely from the plate to the filament/cathode.
The fact that the current flows from plate to cathode while the electrons flow in the opposite direction, is just another instance of conventional current formalism.

But in conventional current, does anything actually flow?

 

[GoldDigger]

But in conventional current, does anything actually flow?

Sure. Conventional charge.
One of the few places where the actual sign of the charge carrier matters is where the individual charged particles hit something, like a phosphor. Or where a particle beam is deflected by a magnetic field.
Interestingly, the simple triode tube is another example, in that the ability of a small voltage at the grid, located close to the cathode, to modulate the current corresponding to the higher voltage, but more distant plate depends on the charge carriers being electrons emitted from the cathode.

 

[gar]

140824-0951 EDT

mbrooke:

You are still confusing the mechanism by which electric current flows with a tool for analysis.

When an electrical circuit is drawn on a piece of paper consisting of a battery, switch, and a resistor all connected in series is there any current flow in that black line on the paper? No. But I can define the direction of current flow in that circuit by some agreed upon definition, and in turn do a calculation on how much current would flow in a real circuit, yet there is no flow at all in the paper.

Just disassociate the definition of "conventional current" from the actual mechanics of the real current flow.

.

 

[Besoeker]

But in conventional current, does anything actually flow?

Electrons. Drift rather than flow.

 

[rt66electric]

I'm positive

I'm positive

I have the universal definition, that combines electronic theory, electrical theory, chemical valance, electromotive force, magnetic force, ring flow theory, and others....

I'm Positive that the earth SUCKS and electricity is ANTI-SUCK

:lol::lol::lol:

 

[charlie b]

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.

 

[Jon456]

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.

To take this visualizing concept one step further, don't think of it as an "electron hole" moving in the direction of conventional current flow, but rather think of it as a positively-charged atomic nucleus. Physically, the nucleus is not moving. But the propagation of positive charge is.