[Amps] "Conventional" current flow

[Jerry O. Stern]

Hi Jim

Great explanation as always.  So if "flow" is a mathematical construct, in
the early days of modern electricity why did the great fathers arbitrarily
pick current flow opposite of electron movement?  Couldn't they have
reversed it and maintained the concept at least wrt electrons while
maintaining the same mathematical construct of ignoring the sign of the
charges?  It just seems like an unnecessary non-intuitive notation was
introduced to throw off the non-physicist.
 
73 Jerry
NY2KW (ex-K1JOS) 

-----Original Message-----
From: Amps [mailto:amps-bounces at contesting.com] On Behalf Of Jim Garland
Sent: Thursday, November 17, 2016 12:17 AM
To: 'Mike Waters'; amps at contesting.com
Subject: Re: [Amps] "Conventional" current flow

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. 

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 

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