Re: Laser technology

Aaron wrote:
> David L. Burkhead wrote:
>> "Aaron" <aaronsan@xxxxxxx> wrote in message
>> news:1134676600.501694.93810@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
>>>
>>> Daniel Silevitch wrote:
>>>> On 15 Dec 2005 10:02:22 -0800, Aaron <aaronsan@xxxxxxx> wrote:
>>>>
>>>> How many ways are you wrong in one paragraph? Let us count:
>>>
>>> How many times do you act like an *** in your reply (note that
>>> others did not feel the need to act the same).
>>
>>
>> Since you call pointing out where you are wrong "acting line an
>> ***"
>> you must use a different definition than I do. Welladay.
>>
>
> Really? Allow me to compact the first 6 words of that section of the
> post for you:
> "Wrong. Right. Wrong. Wrong. Wrong. Wrong."
>
> How does it fit your definition now? Note also that said poster freely
> admitted to being an ***, as do I.

It fits my definition of an accurate description of a post that
purported to correct someone else.

>>>>> Did scientists discover that force is transmitted via photons
>>>>> when I
>>>>> wasn't looking? Is that what you are saying?

>>>> EM forces _are_ transmitted by photons.


>>> I still need a cite on this one. I do recall now that light is
>>> electromagnetic, but isn't the above statement saying, for example,
>>> that two like-charged particles repel due to a force generated by
>>> photon exchange? (or some such similar statement)

>>> If this has been discovered, I either missed the discovery (if
>>> recent),
>>> or missed the discussion in classes (if not recent). Hmm.

>> Here's one cite (of a very great many):

http://faraday.physics.utoronto.ca/GeneralInterest/Harrison/HighEnergy/HighEnergy.html

>> Note that the photon as the intermediary for electron-electron
>> scattering is treated as completely routine, not as some great
>> discovery on
>> the bleeding edge of theory.

>> Here's another cite that gives a bit of history:

>> http://hyperphysics.phy-astr.gsu.edu/hbase/forces/qed.html

>> Note that Richard Feynman was awarded the Nobel Prize for
>> figuring this
>> out back in 1965.

>> [ 8< ]

> Thanks.

>>>> (and one nonsensical
>>>> parenthetical comment).

>>> Are you shitting me? You didn't understand my complaint about the
>>> invention of "holes," because some people don't like dealing with
>>> negative charges? I'm particularly rabid on that subject, true, but
>>> I
>>> know I'm not alone in wondering why the *** we couldn't just all
>>> deal
>>> with electrons, from the beginning.

>> Actually, the most common use of holes as charge carriers that I
>> am
>> familiar with is in doped semiconductors. In pure silicon or
>> germanium, the
>> crystal lattice has every electron position filled with no electrons
>> left
>> over (major part of the reason these two elements are such poor
>> conductors).
>> When doped one way, you get a crystal lattice where every position is
>> filled, but with some electrons left over (N type) and when doped
>> another,
>> you get a crystal lattice where there are "missing" electrons (P
>> type).
>> It's these places in the crystal lattice where the electrons are
>> "missing"
>> that are called holes. Now, looking at either type by itself,
>> there's
>> nothing much to chose from between calling a current the migration of
>> electrons or the migration of holes. However, when you start
>> looking at
>> junctions, you get migration of charges across the junction in a
>> pretty
>> narrow band. When you start looking at those in an actual
>> quantitative type
>> of way (as engineers do when they're designing semiconductors) it
>> gets a lot
>> simpler to start thinking in terms of "majority carriers"--which are
>> electrons in N type semiconductors and holes in P type. That's
>> where the
>> idea of "holes" comes from, not "we don't want to deal with negative
>> charges."

> Right. I had forgotten that holes are essential in explaining
> semiconductors.

>> You may, however, be thinking of "conventional current" which
>> basically
>> treats current as if it were the movement of positive charge rather
>> than
>> negative. That, however, is more historical than anything else.
>> People
>> started working with electric current and charge before they even
>> knew that
>> there was such a thing as an electron. Scientists of the day
>> figured out
>> that current was charge moving, but had no way of determing the
>> sense of the
>> charge that was moving since, to any means they had at the time to
>> measure
>> it, a positive charge moving to the left behaved exactly like a
>> negative
>> charge moving to the right. So they just picked one. A lot of the
>> early
>> work was done using that convention of positive charges being what
>> was
>> moving and so it remains in the lexicon.

> This is what I was really referring to. I understand the reasoning
> behind it. I prefer to use reality instead of convention.

What you fail to realize is that a lot of important work was written
before anyboy had any knowledge of the existence of electrons, protons,
neutrons, or anything else. Someone wanting to read Ampere's work, for
instance, needs to understand the use of conventional current.

On the one hand you have important historical work written with conventional
current. On the other, you have important _modern_ work (semiconductors)
where dealing with the movement of notional positive charges (holes) is
important for understanding their operation and so being comfortable with
that concept is likewise important. On the third hand, being able to think
about how, for most purposes, you could consider current to be negative
charges going one way or positive charges going the other helps to
understand the importance of things like the Hall effect (where the sense of
what's flowing does matter).

Given those factors, the retention of conventional current within the
eletrical and electronic engineering community is not only reasonable but a
positive benefit. In no case does it derive from any "we don't want to deal
with negative charges." That claim was, and remains, nonsense.

With very few exceptions (relatively speaking) nobody measures electric
current by measurement of individual electrons (Millikan being the first in
that line) both Electron Current and Conventional Current are tools used to
describe current, no more and no less. Thus your self-righteous "I prefer
to deal with reality rather than convention" is like talking to a carpenter
and saying "I prefer to deal with hammers rather than saws."


--
David L. Burkhead "May I be just half the person
mailto:dburkhuad@xxxxxxxxxxx my dog thinks I am."
My webcomic Cold Servings
http://coldservings.keenspace.com
Updates Wednesdays


.