I migrated it over to Chat with a copy&paste but I never found the symbol that looks like "A". I lost the BOLD and I lost the functionality of the hyperlink. I hope you can fix those errors.

I don't intend to modify this in the future and find your carefulness puzzling. This article has been gathering cobwebs on my hard drive for years because I feel that is pretty much finished.

Anyway, glad to be helpful. Try to keep the trolls off it. Thanks for your help.
I leave it in your hands now.

 

The other inquiry that keeps popping up from time to time is the question about

voltage
voltage drop
voltage across
voltage at

http://forum.allaboutcircuits.com/showthread.php?t=56372

 

Mr Chips, I find that subject much more difficult than what I wrote about. You are welcome to give it a try!

 

Just give us two posts on the thread, we can fix it from there. For now I'll erase the existing thread, as that one will accumulate posts. People can't help themselves.

 

Yay! It's a sticky.

Ironically, I have never read the stickys!
On the other hand, now we can send noobies to read it without going off-site.
After sending 4 of them to Electrotech in one week, I began to think I should post it here.
Thanks for the help, Bill.
I hope many good noobies get a handle on basic theory because of it.

 

I have found 3 types of beginners (my preferred term, I think it shows more respect). Those who hate reading, and will happily burn up parts until they have to read, those who will reluctantly read because they have to and can't afford to burn up parts, and the ones who understand that reading is part of the process.

The article is a bit long, but I don't directly hold that against it. It is going to be a bit off-putting for the first 2 classes, the 3rd will have read enough other literature they will have it down. I am going to see if there is much reaction to it one way or another.

It might be worth while adding a section on voltage drop, since the subjects are closely related.

 

Refer to post#23

In addition, I think the beginners should be the judge of whether it is too long, not the old veterans. Us old guys can absorb that information in a blink. New guys need to digest it. THEY are the best judge of whether it is too long.

 

A trick my Dad taught me for writing is maximum verbosity, then ruthless culling. If a sentence, phrase, or paragraph doesn't serve a definite purpose, then lose it. After a while I got to where I do it automatically. It is something everyone has to learn for themselves though, it is best learned by practice.

It basically works for all writing.

 

I agree. I cut some really cute stuff out of that because cute was interfering with the goal, and still, it's a bit long. If the beginners complain, there is still room to trim some.

 

This is in response to the query as to why nobody has bothered to define the terms "voltage drop".

"voltage drop" is an in-crowd expression that nobody has to define because we all understand what it means. Here is the lowdown.

It is like "distance". We do not define it because we know what it means.
Saying "The distance at New York City" has no meaning,
whereas "The distance to New York City" has a specific meaning.

"voltage at ..."
"voltage across ..."
"voltage drop ..."
"voltage drop across ..."

"almost always" mean the same thing.

Voltage is a measure of potential difference. It is always the voltage between two points. That is why a voltmeter has two connections. It is the potential at Point A with respect to Point B.

Take a look at the circuit diagram above for illustrative purposes only.
Saying the "voltage at R1" is ambiguous, while "voltage drop across R1" means (V1 - V2).

When we say "the voltage at R2" we really mean the "voltage drop across R2" which would be (V3 - VGND). If VGND = 0V then most of us would understand "the voltage at R2" to be equal to V3.

The "voltage drop" at D1 would be (V2 - V3).

If someone said the "voltage at D1" or the "voltage at the base of Q1" we would understand that to mean V2.
Why? Because when you understand circuit topology we know that in this case we are interested in the voltage at this important node with respect to VGND.

Saying "the voltage drop at the base of Q1" is not meaningful, like saying "the distance at NYC."

It's good to be part of the in-crowd.

 

from ( closed ) ( sticky ) Ohm's Law for Noobies...or The Amp Hour Fallacy

"Whenever two photons combine, they make an electron."

could use a touch up, I have trouble finding a Feynman diagram for this, perhaps because it violates charge conservation.

I assume the author can edit it.

 

http://physics.bu.edu/~duffy/PY106/PhotoelectricEffect.html

Maybe this article from wiki might shed some light.

 

Actually this is a good point, a photon is emitted when an electron drops a energy level, and is absorbed and causes a electron to raise an energy level in its "orbit". I have never heard an electron being created by two photons.

This is the core source of lasers. You will note when an electron emits a photon, it is still an electron, but is now at a lower energy level.

Source please?

 

I could be wrong. I don't remember where I picked that up. I do believe that "this planet is fairly slopping over with spare electrons". Any suspicion that I'm wrong on that one, too?

Fear not. I am completely willing to change anything that is actually wrong.
I'm gonna see if I can find steveb. I think he is likely to know the answer.
Anybody else likely to know the answer? (Suggestions please.)

Edit: Sent PM to steveb

 

My analogy, and it is an analogy, is we are living in an ocean of electrons. They are not spare, but they are so numerous that they can move around easily in large numbers. Things like storms provide energy to move them in vast numbers.

Make your changes to the master copy, preferably highlight it in red, and I will transfer it to the sticky.

 

I could be wrong. I don't remember where I picked that up. I do believe that "this planet is fairly slopping over with spare electrons". Any suspicion that I'm wrong on that one, too?

Fear not. I am completely willing to change anything that is actually wrong.
I'm gonna see if I can find steveb. I think he is likely to know the answer.
Anybody else likely to know the answer? (Suggestions please.)

Edit: Sent PM to steveb

Somehow I missed this thread. I've been tied up with some urgent work lately. The intent and content of the article is good and interesting, although I've only had time to scan it quickly, but it looks good.

On this issue of photons creating electrons, I agree with the others that this is not a true effect. For this discussion, I think we can ignore the details of particle physics and forget about all the ways an electron may be created, where none existed before. As far as we are concerned here, we can say that the electrons we deal with are pretty much there to begin with in matter, starting as electrons orbiting atoms. They just get moved around - either deliberately by us, or haphazardly by nature.

In one sense, photons can be used to dislodge electrons from a conductor (photoelectric effect). Also, a similar thing happens with thermionic emission. Also, the electrons that conduct in a wire are free in the sense that they are not tightly bound to any one atom, so they move around when fields are applied.

Getting to the core of the matter, hole electron pairs can be created in a semiconductor, and this is probably the closest thing we can think of for photons creating electrons. But, this is just a quantum effect where the created exciton appears to be a real pair of particles, even though they are not true particles. The key difference is that there is no violation of conservation of mass/energy and charge. But, that is a very interesting and useful thing to us here, hence a simple clarification about this point is probably all that is needed.

 

I altered post#18 in this thread.
Most of the paragraph under the bold:
How to get Electrons to do useful work:

 

I would like to contest that E = IR is Ohm's law. I would like to have a 30 page brawl about, starting now. GO!

[/sarcasm]

 

The surprise I got here is that after the 30 page brawl on Electrotech, none of those guys spotted the error in fact! (Two photons trying to make an electron.)

(One more "Thanks" for giving me an LOL.)

 

Could you please highlight the changed part (change the color) or quote it. Going between the two posts is a major PITA.

***********************

OK, got it (I think). I put the two articles in the same position on the screen, and clicked back and forth to seek the changes.