Highly descriptive electronics expose site.

[Plectrum]

Just found a really interesting site on the background physics of electronics... very easy to grok, and illuminating. Well... for ppl like me.

http://amasci.com/amateur/transis.html

Grant.

[jrc4558]

For the longest time i thought it's 'to grokk' go figure... (i only read the translation)

[Plectrum]

For the longest time i thought it's 'to grokk' go figure... (i only read the translation)

You're probably right...

Grant

[R.G.]

Interesting site. The guy spent quite some time in doing that. Unfortunately, he got some things at least novelly incorrect.

The good:
- the idea of pre-filled hoses; I never had a problem with this, but apparently some people do
- the idea of batteries, power supplies, alternators, etc as pumps, not charge sources; I used that one in my intro to electronics at GEO.

The trivial restatements
- That charge flows, not current; this is a bit of unnecessary sophistry, as current is defined as a movement of charges. So current flowing, charges flowing - what's the difference? But it's OK to think of it that way if it helps you, just like for all practical purposes thinking of the moon as made of green cheese is not fully accurate, but works for most practical applications.
- the "sea of electrons", everything already full of them is taught in every good introductory physics and EE materials course. I guess you might miss it if you were completely self taught. Apparently the author did.

The wrong:
- we don't find them often, but there are true charge squirters around. Corona effect can literally spray electrons away, thermionic emission does this in vacuum tubes, and static electricity injects charges into something mechanically. But it's OK to think of normal electronics as ferris wheels of charge moving about.
- The difference in insulators and conductors; all everyday matter is composed of a central nucleus that's positively charged and electrons conceptually orbiting the nucleus. The electrons weight substantially nothing compared to the nucleus. Moving electrons is easy, moving nuclei is hard. Depending on the kind of nucleus, it is easier or harder to remove electrons, which must be removed from the outside in. In some materials, particularly metals, the outside electrons are so freely shared between like-nuclei that almost any electrical field shove will shove them from one nuclei to another one. That is, the electrons are pushed along from atom to atom easily. The exact amount needed to push one electron from one nucleus to another varies from atom to atom. It's easiest in silver and copper, and gets harder with different metals. Some make it difficult, but possible. these are the semiconductors like carbon, silicon, germanium, and so on. Some make it really, really difficult to tear an electron off and push it somewhere else. Because it is so difficult, we give up and call these insulators. The relative difficulty of pushing an electron from one atom to the next determines the resistivity of the material. Metals make it easy. Air and other gasses make it hard because the electrons are tightly bound in unionized gasses. Vacuum makes it really hard, because you have to push hard enough to push the electrons out into free space, no nuclei bridges to push to.
- the difference between silicon and metals: silicon by itself is almost an insulator - very hard to push an electron along. When we DOPE silicon, we do it with materials that either have more outer electrons than silicon or fewer. The dopants with more electrons bind to the silicon, but have a spare outer electron that can be pushed around easily since it's a loner. These dopants make for N-type silicon, because the electron carries a negative charge. Nuclei with one fewer outer electron than silicon do the same thing, but make one of its silicon neighbors have a scarcity of electrons, making a "hole" or the absence of an electron. It turns to be easy to push an electron into that hole - but that creates a hole one space over. So you get hole flow, and a P type material. Silicon an other semiconductors offer us the ability to custom design a material with (1) a selectable number of available electrons to move around and (2) different internal types of conductors - holes and electrons. We can manipulate the electrons flowing through by varying the electric field force around this stuff. 
- the idea that the transistor is controlled by base-emitter voltage; purely wrong. It's how many charge carriers you insert to spoil the BC depletion regions ability to hold off conduction.
Actually, I guess I could put this up in "trivial restatements". You have to change the voltage on the BE to inject current, and injecting current raises the voltage.

in either case, the part two stuff is OK - injecting charge erases the static depletion region at the base-emitter and lets current through the top base-collector region, but the method is injecting charge into the depletion region.

[mac]

The trivial restatements
- That charge flows, not current; this is a bit of unnecessary sophistry, as current is defined as a movement of charges. So current flowing, charges flowing - what's the difference? But it's OK to think of it that way if it helps you, just like for all practical purposes thinking of the moon as made of green cheese is not fully accurate, but works for most practical applications.

I agree with you that for practical purposes "this is a bit of unnecesary sophistry".
I guess that the author wanted to say that current is defined as charge flowing per unit time and current flowing is charge flowing and flowing. In mathematical language charge flowing is i = dq/dt, and current flowing is di/dt = d(dq/dt)/dt = d2q/dt2.
Analog to space, velocity and acceleration.

mac

[R.G.]

The way I was told the story, current is the rate of movement of charge - that is, current in amperes is coulombs per second.

In fact, I was told that the ampere was DEFINED as being one couloumb per second. d^2Q/dt^2 would then be the rate of change of current.

Coulombs can be separately defined as a specific number of electrons, or as a mechanical force between plates charged to a voltage, so I've always thought of amperes as a derived unit, not a fundamental unit like coulombs are - in my head at least.

I guess if the idea that current is the second derivative of charge with time is what the author anctually meant, then that's another one for the "dead wrong" category.

The electrical articles there seem to be grasping for some fundamentally different way to talk about electricity. Maybe he's after some kind of teaching aid for people who can't get the normal explanations, or people who have missed some of the first steps. Or perhaps he's found his own separate and beautiful reality somehow.

[puretube]

http://en.wikipedia.org/wiki/Ampere

[mac]

I guess if the idea that current is the second derivative of charge with time is what the author anctually meant, then that's another one for the "dead wrong" category.

I wish to think that a guy that read R. Feynmann can not make such a mistake

mac

[R.G.]

I wish to think that a guy that read R. Feynmann can not make such a mistake

I wish to believe that as well, so it brings me no pleasure to see what he's written.

Like I said, perhaps it's just that I do not understand the terms he's trying to use, or that he's grasping too hard to be different.

http://en.wikipedia.org/wiki/Ampere

OK, so the ampere is more basic. A Coulomb is equal to the charge moved by one ampere in one second, or 1A*1S=1C, or 1A=1C/S, which is close enough to my working definition, I guess. 

[A.S.P.]

glad I just found on the web,
what I thought to remember having been taught
a few decades ago at the Ohm-Gymnasium
(yes, he`s the most famous son of our town...):

the Silver-Ampere;

(actually, I had that silver in mind a few days ago when I found that "Wiki"-definition,
and was wondering a little about that.
I can`t say I`m a Wiki-friend or blindly believer...).

http://www.sizes.com/units/ampHist.htm

[calpolyengineer]

Umm, current IS the first derivative of charge with respect to time.
 
Also, he is right that current doesn't flow, because current is defined as a flow of charge. Think of it as a river. The water molecules would be the charge, and the speed of the river is the current. Would you say that the speed of the river is flowing or that the river is flowing? That is what the author means.

-Joe

[johngreene]

The wrong:
- we don't find them often, but there are true charge squirters around. Corona effect can literally spray electrons away, thermionic emission does this in vacuum tubes, and static electricity injects charges into something mechanically. But it's OK to think of normal electronics as ferris wheels of charge moving about.

charge squirters is the name of my new band.

--john

[R.G.]

Umm, current IS the first derivative of charge with respect to time.

Yep, 'swat I said.

Also, he is right that current doesn't flow, because current is defined as a flow of charge. Think of it as a river. The water molecules would be the charge, and the speed of the river is the current. Would you say that the speed of the river is flowing or that the river is flowing? That is what the author means.

As I said,

- That charge flows, not current; this is a bit of unnecessary sophistry, as current is defined as a movement of charges. So current flowing, charges flowing - what's the difference?

It's true that current is itself a movement, and talking about a movement of a movement is very odd. However, finding someone that has not been extruded through a physics course recently that would make that distinction is going to be very difficult. In the common use of the language, speaking of current flowing is not perfectly accurate - it's just what everyone understands. I actually can't remember anyone being confused by the difference  in a long, long time. Hence my comment about an unnecessary bit of sophistry.

To be absolutely correct in great detail, what flows is electric field *and* charge carriers. The electric field changes in the conductors move at a substantial fraction of the speed of light, on the order of half, and the electrons and holes move much more slowly. Electron and hole mobility in conductors and semiconductors is tremendously lower than that. But electricity *acts* like it flows at the speed of light. I personally would not like to be presented the task of teaching a group of the uninformed about why when I attach a battery to a wire ...here... that the electrical signal appears at the other end of the wire at about one nanosecond per foot; however, the electrons only move along at a much slower rate.

[Skreddy]

The idea of a pipe filled with identical marbles is a good teaching aid.  A marble added to one end of the pipe appears virtually instantaneously at the other end, even though each individual marble only moves a tiny bit and doesn't need to be all that fast.

[mac]

Everything you always wanted to know about Classical Electrodynamics but were afraid to ask...

John David Jackson, Classical Electrodynamics, John Wiley & Sons, Inc.

Not an easy book to digest but one of the best. Anytime the author states "it is easy to demonstrate that..." prepare yourself for a sleepless night filling 10 pages of jerogliphics. Not recommended for RG's group of uninformed students

A more friendly but rigurous book is

LD Landau and EM Lifschitz, Electrodynamics of Continuous Media, Pergamon Press.

OK. OK. I know. These books are for those with some formal education or at least with some calculus knowledge.You won't find any reference to a Fuzz Face, germanium transistors, electronic devices, or how a transistor really works... something I don't figure out yet!   

mac