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Author Topic: Actual vs conventional current?  (Read 3717 times)

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Offline zamboniman60Topic starter

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Actual vs conventional current?
« on: April 06, 2007, 01:47:09 PM »
When you people are visualizing what schematics do in your minds, do you find it more useful to imagine conventional (+ to -, useful because ALL THE ARROWS ON TRANSISTORS AND DIODES MAKE SENSE) or actual (- to +, what really happens) current? A pet peeve of mine is the fact that many books on electrical engineering never mention conventional current whatsoever, and don't explain why diodes and transistors have their arrows pointing the way they do. Which do you think should be taught?

Offline Admin

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Re: Actual vs conventional current?
« Reply #1 on: April 07, 2007, 03:12:10 AM »
Although this isnt correct, I imagine electrons moving from + to -. (yes, I actually do picture the electrons because it helps me understand the circuit).

This is only because it fits the convention and arrows and such.

This should be the way its taught, but only because it matches convention . . . it gets really confusing otherwise . . .

Offline zamboniman60Topic starter

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Re: Actual vs conventional current?
« Reply #2 on: April 07, 2007, 02:36:44 PM »
I'm glad to hear that I am not completely insane to imagine electricity as a flow of holes from + to -. I've been reading this 1970's navy manual on electronics (useful so I can understand how to use tubes), and they have a really annoying habit of changing from actual to conventional current and back with no warning whatsoever. I suppose it's no less confusing than "ravel" and "unravel" meaning the same thing... Or flammable and inflammable, or thaw and unthaw.

Offline dunk

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Re: Actual vs conventional current?
« Reply #3 on: April 08, 2007, 08:58:12 AM »
i believe the reason for this is historical.
scientists used to think electrons moved from +ive to -ive. that's why the symbols got drawn that way round.
it would have made sense to early scientists i guess. why else would it be the +ive terminal that gives you an electric shock?

dunk.

Offline Joe

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Re: Actual vs conventional current?
« Reply #4 on: April 08, 2007, 11:59:39 AM »
I had one teacher that said it makes no difference whatsoever, and that the only thing we can see anyway is polarity, so therefore that is all that matters. For the engineer, I think this is pretty much true. Only when studying components at the physical level (as in the physics of how they work) is it necessary to think in terms of electron flow (neg to pos) to know why capacitors, for example, do not charge to the opposite polarity.

Offline Tsukubadaisei

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Re: Actual vs conventional current?
« Reply #5 on: April 09, 2007, 01:27:14 AM »
i believe the reason for this is historical.
scientists used to think electrons moved from +ive to -ive. that's why the symbols got drawn that way round.
it would have made sense to early scientists i guess. why else would it be the +ive terminal that gives you an electric shock?

dunk.

Yes the reason is historical. The concept of current was developed by B. Franklin (hope it is correct) and by that time they believed that the moving charges were the positive ones.

I had one teacher that said it makes no difference whatsoever, and that the only thing we can see anyway is polarity, so therefore that is all that matters. For the engineer, I think this is pretty much true. Only when studying components at the physical level (as in the physics of how they work) is it necessary to think in terms of electron flow (neg to pos) to know why capacitors, for example, do not charge to the opposite polarity.

Your teacher is partially correct because the direction of the current and the direction of the electron flux are opposite. If you are dealing with magnetism it doesn't make any difference. But when you are dealing with quantum physics it is very important to know what is actually moving. If you try to study how to build a transistor you will understand.

A pet peeve of mine is the fact that many books on electrical engineering never mention conventional current whatsoever, and don't explain why diodes and transistors have their arrows pointing the way they do. Which do you think should be taught?

The arrows point the way they do because the traditional definition of the current direction. If you want to anderstand more about active circuit parts like diodes and transistors you should then research in an electronics or quantum physics book. I think the conventional current is easier to deal with because it is easier to calculate( you don't have to worry about the - (minus) during the computation). If you really want to have a concrete image of what is really happening inside the circuit you can just forget about the electronic movement and instead consider that the moving Charges are the positive holes moving in the same direction of the electrical current. Actually this way of thinking is extremely important when dealing with semiconductors.
A.I.(yes those are my initials)

 


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