Re: Grid #2 in ultralinear mode


"flipper" <flipper@xxxxxxxx> wrote in message
news:qc4bt1ls0plfkrenkctm7aj94ahik1mof8@xxxxxxxxxx
> On Tue, 24 Jan 2006 01:56:54 GMT, "Ian Iveson"
> <IanIveson.home@xxxxxxxxxxxxxxxx> wrote:
>
>>
>>flipper wrote
>>>>
>>>>But...but...the necessary pressure vessel fills up with
>>>>steam...and
>>>>the valve doesn't fill up with electrons.
>>>>
>>>>OK they have equilibrium in common. Wondering what else...change
>>>>of
>>>>state? Latent heat?
>>>
>>> Any analogy can be drawn to absurdity by expanding it past the
>>> limited
>>> scope the analogy intended to address, which is what you're
>>> trying
>>> to
>>> do with that one.
>>
>>No. If an analogy only has one thing in common, it is a worthless
>>analogy.
>
> Nonsense. 'One thing' in common is perfectly fine if the purpose
> is to
> illuminate that 'one thing'.

Nope, since the "one thing" is already spoken for, there must be
other things to do the illumination. Another way of putting it, the
"one thing" analogy brings nothing new to the explanation, since
that one thing was there already. *All* the other things attached to
it become potentially misleading, extraneous baggage.

>> Of course it would not be an analogy if it were the same in
>>all respects...I'm not asking for that.
>
> Near as I can tell you are. Regardless, you're trying to extend it
> beyond it's applicability.

I am trying to find where its applicability lies, by process of
elimination.

>> More than one thing would
>>do.
>
> What's relevant is whether the analogy works for the purpose it
> was
> made and, in that context, it does work fairly well.

As I agreed, once I re-jigged reality to fit :-)

>>>>Right...dimly remember encountering the eV...odd how the
>>>>electron
>>>>gets its very own unit of speed.
>>>
>>> Not really, it's a matter of unit convenience but, at any rate
>>> (pun),
>>> eV isn't velocity, it's energy.
>>
>>Yes of course, that's why it seemed odd to use it to answer a
>>question about speed. Ask a straight question about an electron,
>>and
>>you will rarely get a straight answer.
>
> You misunderstood the 'answer' you were given. He said nothing
> about
> eV being 'speed' or 'velocity'. He said electrons accelerated
> through
> 25KeV would reach relativistic speeds but that is no more a
> statement
> of eV *being* 'a speed' than someone pointing out you'll reach a
> dangerous velocity falling off a cliff is some kind of claim that
> the
> earth's gravitational constant is 'a speed'.

No, not Chris, I meant what I learned at school. And what is still
in my school physics book. It involved an assumption about the mass
of the electron...I'm sure we all know the difference between speed
and energy.

Your analogy is false. The gravitational constant is not an
expression of energy. I can play that game too.

> He merely said 25KeV is sufficient energy to do it.

Do what?

>>>> I remember when I asked "What's
>>>>that in mph?", much handwaving would ensue. That must have been
>>>>because of the change in mass, possibly at a time when it was no
>>>>more than a dark suspicion that something was amiss. Presumably
>>>>that's there to stop the electron travelling faster than light?
>>>>
>>>>If I ask how fast electrons travel in a vacuum between cathode
>>>>and
>>>>25kV anode, and the answer is 25keV, I'm not sure I feel
>>>>enlightened. Now I know about relativistic mass I feel much
>>>>better
>>>
>>> eV is energy and (kinetic)E= .5mv^2
>>
>>Speed or velocity? I raise the point because we normally think of
>>energy as scalar, and voltage as a vector.
>>
>>Anyway, yes of course, that's why I said I felt much
>>better...because given the energy, I thought I also needed the
>>mass
>>to work out the speed or velocity.
>
> I have no idea what you're trying to complain about. Electron rest
> mass is known, at least well enough.

You have lost the original sense. I notice you are not answering my
questions BTW. You are skipping them to niggle about your
misunderstanding of what I am saying. I was complaining about the
use of eV as an expression of speed. Mass is required for the
conversion. Problems ensue unless mass is a variable, however, for
otherwise, given a great enough potential, an electron would exceed
the speed of light.

Here, for me, the whole shebang becomes a matter of definition...of
compliance with other definitions...of coherence. Hope of absolute
truth is lost.

>>> eV is convenient for particle physics because it is also the
>>> case,
>>> for
>>> this purpose at least, that E=MC^2. Energy has the units
>>> (mass)(length)^2/(time)^2 so divide by C and you get momentum.
>>> Divide
>>> by C again and you get mass (old style "relativistic mass"). Lay
>>> confusion stems from the particle physicists use of shorthand
>>> 'apparently' calling all three eV with the divide by C
>>> 'understood'
>>> when speaking of momentum and by C^2 'understood' when speaking
>>> of
>>> mass when, to be precise, it is eV/c and eV/c2 respectively.
>>
>>Yes, this is the kind of loose usage I was complaining about.
>
> Well, you can either complain or understand it and I suggest that
> the
> latter is more productive than expecting all the physicists in the
> world to alter their common behavior.

Eh? But you were complaining about it...I just agreed with you.

I like to complain *and* understand. The two seem to go together
quite nicely.

As for all the physicists in the world, you are beginning to suffer
from Turneresque delusions. You haven't a clue what all physicists
think. Consensus, maybe...although a rather ragged one. Anyway,
physicists are paid to question theory, not agree with it.

Even if everything about the electron is agreed by "scientists" (why
assume I am not one, BTW, and what about philosophers...don't they
get a look in?), then surely you would wish that consensus remain
open to question? Isn't that what science is supposed to be?

>> Also I
>>am pretty much bound to object to this changing mass lark but I'm
>>stuck for an alternative.
>
> You're not alone and modern physics doesn't use that 'analogy'
> for
> much, any more, other than for the purpose of an analogy, which is
> why
> I added the (old style "relativistic mass").

So what happens now, in your world, to stop an electron accelerated
through a large potential from exceeding the speed of light?

>> Stalin killed our scientists before we
>>found out :-(
>
> Should have been plenty of time to grow new ones by now.

Where? Science requires community, not just to ensure sufficient
diversity for evolution, but also to protect itself from
persecution. Materialism is still a politically unacceptable
standpoint for the dominant ideology.

>>> Path length is implicit in the eV term. Place a charge on two
>>> plates
>>> so you have a particular eV. Change the spacing and eV changes.
>>
>>What? Run that past me again please, slowly.
>
> Make a capacitor with movable plates. Charge it to a particular V.
> Move the plates further apart or closer together. V changes.
>
> Put wires on the plates and mound it in a cylinder suitable for
> hand
> holding and you have a condenser microphone.

Eh? You said eV changes...we were talking about the energy of
electrons passing from one electrode to the other, remember? Like in
a thermionic valve. You said path length is "implicit in the eV
term". Now you have dropped the "e". That's a bit naughty of you I
think.

>
>>> "Potential difference" is the energy required to move a charged
>>> particle from one potential point to the other against the
>>> applied
>>> electric field. Let it 'free fall', I.E. be accelerated by that
>>> field,
>>> and it acquires the energy.
>>
>>Right.
>>
>>> Which get's back to eV being energy.
>>
>>What, again?
>
> eV is energy.

And again...


>>>>Also I wonder now if I should be considering velocity rather
>>>>than
>>>>speed. Do they all arrive with the same velocity normal to the
>>>>screen, and so at different speeds depending on angle?
>>>>
>>>>One thing I have learned from all this is that electron flow is
>>>>coherent in a valve, otherwise the screen couldn't be hidden in
>>>>the
>>>>shadow of the grid.
>>>
>>> You don't need 'coherency' to cast a shadow and all one need do
>>> is
>>> look at their own shadow on a sunny day to confirm it as
>>> sunlight
>>> isn't even monochromatic, much less coherent.
>>
>>You most certainly do need coherence to cast a shadow. Perhaps you
>>have a specialised meaning of coherence in mind...possibly germain
>>to this subject...like phase coherence, in which case I apologise
>>for misleading you.
>
> I see, well, when delving into the realm of particle physics,
> especially in this day and age of lasers, people are likely to
> think
> you mean to include phase coherency when you toss out "coherent."
>
>>I just mean coherent in the loose sense of an orderly structure.
>>In
>>this case that paths are fairly parallel. Although sunlight is
>>also
>>near-as-dammit parallel, it is not quite coherent in the sense I
>>mean. But close, which is why it casts sharp shadows.
>
> Ok. Now I know what you meant by it.
>
>>The cathode of a typical valve is not even nearly a point source,
>>like the sun. And yet it casts shadows. That is all I meant by
>>coherent.
>
> It doesn't need to be a 'point source' because the plate isn't a
> 'point' either and the order comes from them being attracted to
> the
> plate.

Yes, but I think there is more to it than that.

> They want to go ----> that away
> ----> that away
> ----> that away
> ----> that away

Er...:-) LOL !

Yes, that's probably what I mean :-) I guess the strongest field is
in the direction of the nearest point...although this is a rather
idealised view otherwise I suspect "hot spots" would be more common.
But there are magnetic effects too, and the tendency for electrons
to repel each other.

> and if they make it past the grid they'll have a clear shot (give
> or
> take a few secondary forces) if the screen wires are in the same
> 'path' as the grid wires were.

Of course, as long as paths are parallel...or near enough for the
shadow to be significant. I think it's pretty blurred actually, for
all sorts of reasons, including diffraction.

>>>> I have tried looking this stuff up, but I find
>>>>either what I already think I know, or stuff that appears pretty
>>>>unknowable. Once I get to relativity I wonder if I might be
>>>>better
>>>>of with the "swarm of bees" hypothesis.
>>>>I notice in passing that the CRT transposes the names of screen
>>>>and
>>>>anode, compared to the tetrode:-)
>>>>
>>>>Us materialists are an awkward lot. Or rather, since it is so
>>>>long
>>>>since I met another, (perhaps I am the last?), me materialist is
>>>>awkward. Clearly a vacuum is totally out of bounds.
>>>
>>> A vacuum is simply a place devoid of materialists ;)
>>>
>>>> So, thinking
>>>>again, I quite like this steam thing. The electrons are stayed
>>>>by
>>>>pressure of ether,
>>>
>>> no
>>
>>Oh, don't be such a spoilsport...why not?
>
> Einstein

What...didn't he believe in the ether? When did he say that?

Do you believe in vacuums?

>>>> into which they evaporate when excited,
>>>
>>> They acquire enough energy to escape the electrical forces in
>>> the
>>> atomic structure.
>>
>>Atomic, molecular, electrostatic, whatever...it's metal. Easier to
>>say they acquire enough energy to part significantly from the bulk
>>material.
>
> If you like "bulk material" better than "atomic structure," ok.
>
>> I was trying to stick to the steam analogy anyway...you
>>are miles from there now.
>
> Not at all. When boiling water the water molecules acquire enough
> energy to escape the attractive forces in the "bulk material." So
> do
> the electrons.

Oi! My "bulk material" isn't far from the analogy, I know that. Your
"atomic structure" was.
>
> But, since electrons are negatively charged atomic particles of
> extremely low mass, and water molecules are not, that's about as
> far
> as the analogy goes. But then, that is as far as it is intended to
> go.

No, I like it now! The whole pressure vessel and all...fits with the
ether ;-)

>>>> to which
>>>>they lose energy,
>>>
>>> Energy decay by quantum emission.
>>
>>Oi! I'm a materialist. No quantum nonsense please. Of a photon?
>>What
>>triggers that, or is it a statistical thing?
>
> What 'triggers' a hot body to radiate?
>
>> This is nothing at all
>>like steam!
>
> Why do you have no trouble accepting that 'hot' steam will release
> energy but do with electrons releasing energy?

Release of energy by hot steam is not a necessary part of the
analogy, if it is in an insulated pressure vessel. New steam stops
forming when a surface equilibrium is reached between pressure and
temperature. But you are taking the analogy too far now anyway.

The issue is whether they release energy, or merely convert it from
kinetic to potential, and back again.

>> Not keen on probabalistic explanations either.
>
> Well, I think Schroedinger drew inappropriate conclusions from the
> use
> of statistics but that doesn't alter the mathematics of it.

It was Popper that pissed me off.

>> Are you
>>sure they simply don't achieve escape velocity?
>
> I don't know which 'they' you are talking about but if it used to
> be
> 'locked' to <--- here and is now flying off to --> there then
> saying
> 'they' reached 'escape velocity' sounds like a reasonable analogy.

My little picture is just that the electrons are flung out at less
than the velocity required to escape the electrostatic field, so
they fall back. They don't need to loose energy to do that. OTOH, if
they must be ripped out of an atomic structure, I would expect they
would always achieve enough velocity to escape the field, and would
have to lose energy in order to return. But I'm still hung up on the
surface thing...surfaces are a world of their own. Perhaps the test
is whether they emit photons in the process. Does the ether glow?

>>Again, I don't go along with your atomic structure thing. It's
>>metal...or is it something else?

> Surely you are aware that metals have an atomic structure. All
> elements and compounds do.

Vaguely, ideally, sometimes, in varying degrees. Each metal can have
loads of different structures depending on impurities and formation.
The kind of metal you need to achieve decent perveance presumably
has very little structural energy invested in "outer" electron
positions. Not many materials make suitable cathodes, remember.
Cathode poisoning adds structure because compounds are formed, and
this stops emission.

>> Do your electrons emit photons when
>>they are returned to their "atomic structure"?
>
> Close enough.

Eh?

>> What frequency? IR?
>
> Depends on the energy state they were in and I'm not *that* good
> enough a quantum mechanic to calculate it.

Well it doesn't appear to be visible light...and presumably it's not
dangerous.

>>Anyway, back to the original question, you say that the electron
>>loses its energy by quantum emission. That is an interesting
>>contribution, thanks. I will look it up with respect to the
>>structure of metals!
>
> Doesn't matter if it's metal or anything else. An electron is an
> electron and electrons acquire/release energy by
> absorption/emission
> of quantum packets or, the synonym, photons.

But of course it matters. Not every material makes a good cathode.
My question is whether a change of "energy state" is necessarily
involved, or whether it is just a change in kinetic energy.

They can also acquire kinetic energy, and lose it, without emitting
photons?

cheers, Ian


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