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Re: [Amps] "Conventional" current flow

To: "'Mike Waters'" <>, <>
Subject: Re: [Amps] "Conventional" current flow
From: "Jim Garland" <>
Date: Wed, 16 Nov 2016 22:16:50 -0700
List-post: <">>
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 ma
 ss 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. 


Jim W8ZR


From: Mike Waters [] 
Sent: Wednesday, November 16, 2016 08:15 PM
To: Jim Garland
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) 
flowing from the hot filament to the plate??


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