[Amps] "Conventional" current flow

[Jim Garland]

Hi Mike,

Let me give you the simple, direct answer to your question, and then I will give you the more complicated answer that's closer to being correct. In a vacuum tube, the only things that move between the cathode and the anode are electrons, and these move only in one direction, which is toward the anode. There's nothing else moving inside the tube. Note I used the word "move," rather than "flow," because if we have only, say, one electron or a small number of them, then it doesn't make sense to talk about a flow. A single electron is just a moving charge, it's not a flow of anything. A "flow" always represents the aggregate motion of a large number of things. 

 

Now, what about electric current? Unlike a moving charge, current is always represented as a flow of something. Current flows, it doesn't make sense to speak of current moving. Now, here's the important point. Electric current is an abstract concept. It's not a real substance. You can take an electron and weigh it on a scale (in principle!). You can't weigh current, because current is an idea, not a material thing. Using the language of physics, one would say that current represents the impact of moving charges, but is not the charges themselves. So, in a vacuum tube, electrons move from cathode to anode. The current flow, which is in the reverse direction, isn't a real substance. It's just a useful mathematical way of representing the aggregate effect of the moving electrons. The reason current is so useful is because it allows us to ignore the sign of the charges whose impacts we're describing. It doesn't matter whether the charges are negative, like electrons, or positive, like holes, or a mix of the two. Once you've characterized the impact of the charges as a flow of current, you've learned most everything useful about them. 

 

Here's another example. We know that a variable capacitor passes an alternating RF current. But we also know that no charge actually travels between the capacitor plates. So the current flows between the plates, even though no real particle is moving between them. The abstract idea of RF current flowing through the capacitor is just a useful mathematical way of describing the alternate charging and discharging of the capacitor plates.

 

The universe is an extremely subtle place, and our intuition about it is frequently wrong. When an apple falls from a tree, we say that the gravitational force is pulling it down. But in fact gravity isn't really a force. Einstein showed it is just a distortion of space caused by the mass of the earth. Another example: We learn in high school that a hydrogen atom is a negative electron bound to a positive proton, because unlike charges attract each other. But that's not really true. What really happens is that photons pop into existence and are exchanged between the electron and proton and then disappear. (In physics, these are known as the quanta of the electromagnetic field.) And if that isn't strange enough for you, these photons spend part of their short life changing momentarily into electrons and positrons. These are called "virtual" charges because they're so short-lived, and what's especially interesting is that the mass of these virtual charges is greater than the mass of the photons that created them, thus momentarily violating the conservation of energy. And that's just for starters. Probe more deeply, and things get really, really odd. A vacuum is not an empty space where nothing happens. Particles can pop into existence out of empty space, and then after a short time pop out of existence. (In physics this effect is called the fluctuation of the vacuum state.)

 

So the bottom line is that we shouldn't be troubled by abstract ideas like electric current. Most everything we know about the world is an abstraction of some sort. Instead, we should be grateful that the universe, despite its enormous complexity and subtlety, allows us to simplify its rules into stripped down descriptions that our small brains can understand and that let us do useful things, like build vacuum tubes. 

73,

Jim W8ZR

 

From: Mike Waters [mailto:mikewate at gmail.com] 
Sent: Wednesday, November 16, 2016 08:15 PM
To: Jim Garland
Cc: amps at contesting.com
Subject: Re: [Amps] "Conventional" current flow

 

I just have one more question.

Before I ask it, I need to make clear that my previous questions were based solely on current flow in vacuum tubes. Not wires, not semiconductors, etc. ONLY vacuum tubes.

What --if anything-- is flowing from the anode to the cathode while electrons are flowing from a heated cathode to the anode?

ARE THERE "CHARGE CARRIERS" (or anything else that's real and tangible) SIMULTANEOUSLY FLOWING FROM THE ANODE TO THE CATHODE, while the electrons are flowing from the hot filament to the plate??

Respectfully, 
Mike 
www.w0btu.com