Electron path of travel

[guitarmike2107]

there's no force that can move electrons in the other direction

yes there is, just change the electromotive force, at a basic circuit level i.e. battery and light bulb, just change the battery around and the electrons start moving again in the opposite direction.

[guitarmike2107]

Gravity is a force that can be represented as a vector in a co-ordinate system, change around the co-ordinate system reference and it goes from negative to positive or positive to negative depending on the system chosen.

I think using higher as positive helps understanding when it comes to other theories i.e it's easier to understand positive potential energy than negative etc

[Merlinb]

The mistake people make with the water analogy is to assume that the water represents electric current. It does not!

The water (molecules) represent the charge carriers. Electric current on the other hand, is represented by the visible effect that the moving water has on stuff. When you open a faucet, water gushes out instantly; that is the effect produced by the sudden existence of current. The water itself, however, moves quite slowly. Close the faucet and the current ceases to exist in the pipe. The current itself has no direction; either the water is moving or it isn't. Now, although the visible effects of the current can be viewed as a compressional wavefront propagating towards the faucet, or an expansional wavefront propagating away from the faucet, but both are just the same coin viewed from different sides, so you pick one. Neither viewpoint is 'right' because both are one and the same! That is electric current. The actual direction of the water molecules is irrelevant!

[defaced]

Color me dumb, but you're going to have to draw me a picture on this one. I get the last part of the post, but this first part has got me feeling like a deer in the head lights. Either your nomencalture is screwy and/or physics is being violated (Third Law of Motion), but I'm lost.

The mistake people make with the water analogy is to assume that the water represents electric current. It does not!

The water (molecules) represent the charge carriers. Electric current on the other hand, is represented by the visible effect that the moving water has on stuff. When you open a faucet, water gushes out instantly; that is the effect produced by the sudden existence of current. The water itself, however, moves quite slowly. Close the faucet and the current ceases to exist in the pipe. The current itself has no direction; either the water is moving or it isn't.

[mooreamps]

Color me dumb, but you're going to have to draw me a picture on this one. I get the last part of the post, but this first part has got me feeling like a deer in the head lights. Either your nomencalture is screwy and/or physics is being violated (Third Law of Motion), but I'm lost.

Don't worry about his "nomenclature". Current does have direction through a conductor. The direction of electrical current is dictated by the polarity of the voltage impressed upon the conductor..

-g

[guitarmike2107]

Color me dumb, but you're going to have to draw me a picture on this one. I get the last part of the post, but this first part has got me feeling like a deer in the head lights. Either your nomencalture is screwy and/or physics is being violated (Third Law of Motion), but I'm lost.

it throws me a bit too, Merlin, If current is the rate of change of charge (time based)
, what does charge relate to in water, I always compared pressure/head to voltage, so would rate of change of charge be comparable to flow rate, litres/minute say?

EDIT: also flow rate measurement is non directional, though we know the water flows in a direction

[Merlinb]

what does charge relate to in water, I always compared pressure/head to voltage, so would rate of change of charge be comparable to flow rate, litres/minute say?

Interesting question. Yes, I suppose you could represent charge by the mass of the water molecules, although you're pushing the limits of the analogy!

Charge is a highly abstract concept. It is not a 'thing', but an intangible physical property (which is another reason why current can have no direction. How can a physical property have direction!?!)

The best analogy for charge I can think of, is colour. If you imagine electrons to be like billard balls (they're nothing like that, but hey...) then the charge carried by an electron could be represented by its colour, on a grey scale say. An infinitely positive charge might be pure white, and an infinitely negative charge by pure black. A single electron would be a shade of grey. The presence of a current would be indicated by the change in colour of an infinitely small point, which is why the analogy of a TV screen showing a game of pong is a good one.

To ask "what direction does electric current flow?" is like asking " what direction does colour flow?". The question is obviously nonsensical. It can change either from black(er) to white(er), or vice versa, but direction does not come into it. Current can have a mathematical sign, but never direction.

[defaced]

Absolutely, charge can have a sign and not have a direction. That's called static electricity. Give that static electric case a circuit, and presto, you have flow until the potential difference is neutralized - ie lightening. That is how current is defined, correct? I = dQ/dt, change in charge over a change in time. And that movement is at a speed called the drift velocity. And velocity is a vector, magnitude and direction.

Drift velocity - Wikipedia, the free encyclopediaand my handy dandy college physics book, Amazon.com: Physics For Scientists & Engineers Study Guide, Vol 1, 5th Edition (9780030209727): John R. Gordon, Ralph R. McGrew: Books

[mooreamps]

To ask "what direction does electric current flow?" is like asking " what direction does colour flow?". The question is obviously nonsensical. It can change either from black(er) to white(er), or vice versa, but direction does not come into it. Current can have a mathematical sign, but never direction.

You know what ? You maybe some internet guru and have a bunch guys on bended knee kissing your ring. But, you'd never make in the real world...

-g

[Enzo]

GAry, I don't know, maybe you somehow think it makes your arguments stronger to call people names and otherwise act juvenile, but really, it is tiring. Either make a dissenting presentation or knock off the schoolyard taunting.

[Enzo]

Water is a great analogy because it demonstrates the concept of circuit and flow. Unfortunately for some, if you think of raising a tank of water, which now has to find its way to ground, you are talking conventional current. But the analogy is still useful under smaller focus.


We get hung up here on vacuum tubes. We all know, and there is no controversy, that tubes emit their electrons - whatever they may be - from the cathode to the plate. FIne. What if we look at some circuit like relay trees or solenoid controls. Now we can argue about which way the electrons may flow, but none of those devices work by emitting electrons. You can apply either polarity and a relay will energize. SO then if I run a relay system off +24VDC to ground, I could arbitrarily decide to look at it from electron flow or from conventional current, and it wouldn;t matter. In that case conventional current has our power supply as the source, and is intuitive to that extent. COnventional curent is just a way to look at it. It is not intended to explain HOW tubes work.

If I use a battery to powr a circuit - a wah pedal perhaps - no one here will give a moment's though as to how the battery makes voltage. yet the voltages adn currents will continue to fill our thoughts on it.



How's this for water. You know which direction water is flowing through your pipe, but is that a factor in any calculations as to what the bursting pressure of the pipe might be?

[Wilder Amplification]

I honestly don't see how you CAN'T relate water flow to electric current flow.

Some think a water pump makes pressure. However, this is not the case. A water pump induces flow. Pressure is the product of resistance to this flow.

Just the same, a charge differential between two points induces current flow. Ohm's Law specifically states that voltage is the product of resistance to this current flow.

The issue here is that we have beginners out there who come on these forums to learn. We were beginners once too and as we all know every beginner needs a starting point. Explaining electricity/electronics on the level on which it has been spoken on this forum is definitely not the correct starting point. It's like we've taken a 5 year old and sent him off to college...it just does not work. Beginners cannot grasp the concept of these things until they have the elementary basics down. Simply put...they have to learn to crawl before they comprehend how to walk.

[Enzo]

And that is why the concept of "circuit" is taught with light bulbs, batteries, and switches instead of vacuum tubes.

In a forum like this, we have to be prepared to discuss things at all levels. We can't limit ourselfs to 101 level light bulbs for the novices if we really expect to get anywhere discussing something like parasitics. And we can't just talk over their heads if we plan to communicate anything to them. And what of all those in between. There is plenty of space for discussion of more advanced circuits for folks who understand Ohm's Law and basic tube function, but it need not go so far as load lines and math. Until someone needs that too. of the thousands of posts here, they are legitimately at every level you can imagine.

And we have to decide in each case what our goal might be. It is all well and good to start at the start, on the other hand when we want to give a meaningful response to a question that is just a little over the asker's head, we don;t want to tell him "Oh just go and read the basics for a year and come back." Nor can we tale the time to write a 17 page post that starts at the beginning.

SO we use analogies like water, however imperfect they may be. And yes, conventional current is one of those strategies.

[Merlinb]

I honestly don't see how you CAN'T relate water flow to electric current flow.

You can, but you have to appreciate that the water represents the charge carriers, not the electric current that everyone is interested in.

When water flows in a pipe then we say there is a current. If the water stops flowing then there is no current. So which way does the current flow?
Of course, there is no answer, because current is not a moving object. It is simply a label we give to the phenomenon of the water moving.

It is exactly the same with a marathon. People can move, and flow in a discerible direction. Together they constitute a marathon. But the marathon does not flow anywhere.

[guitarmike2107]

The more I look into this the more I disagree with your definitions

In water, Current is the flow of a quantity, that quantity is measured in litres/pints/cubic metres, 1 Litre = xxx Molocules of H2O (charge carriers)
In electronics, Current is the flow of a quantity, that quantity is measured in coulombs, 1 coulomb = -6.24151 × 1018 electrons (charge carriers)

Both measurements are scalar properties. i.e. don’t have a direction/not vector based.

At a systems level nobody cares what the water molecules are doing and nobody needs to know what the electrons are doing

in a marathon poeple may be the charge carriers, but there is no unit definition for x number of people, if we defined a crowd as being 100 poeple then you could say your marathon had a current measured in crowds/Time.