Wanted: B Level Explanation of Conduction and Resistance

[Dale]

I have to ask who would be actually in this class, what would their level of knowledge be and where would the whole course be preparing them for?

I was envisioning an intro to circuits class. So it would be freshman and sophomore engineering students, assuming some calculus and physics (possibly concurrently with this class depending on the curriculum).

 

[sophiecentaur]

I was envisioning an intro to circuits class. So it would be freshman and sophomore engineering students, assuming some calculus and physics (possibly concurrently with this class depending on the curriculum).

OK. So that means they are likely to get a better version of things later on. The problem is when they don't and end up with a 'mechanical' picture in their minds which is never corrected. Whatever the situation, they should all be given an immense caveat about treating electrons as primary school objects and that you only get 'right answers' to electronics problems with Maths and not with arm waving about little pebbles moving around a wire. It has been my experience that many (probably most) students want to stick with the naive model, rather than moving on and learning to use a bit of problem solving.
I have endless gratitude for Mr Scales who was totally dismissive of the electron model when he taught us A level electricity. As one of his laziest students, I would not have gone for the Maths if he had given me the option.

 

[nsaspook]

You have brought in a very relevant point. Basically, Technicians are 'Trained' to perform certain functions and the training is aimed at being a cost effective way of producing people who will be able to work the technology. The services want people who can 'do the job' and I don't feel that recipients of many courses get a good deal out of them. Electrons and Photons are brought in in an effort to 'explain' the inexplicable (inexplicable with their levels of knowledge). It just demonstrates how difficult a subject Physics is when many of the educationist fail to understand the limits of the simple models they are using. I assume that, as you had a rigorous electronics education, you appreciate that electrons only need to be considered when you're inside some components.

When I started my education electrons in tubes were still very common so we learned the basic rules of tube operation in a way that was consistent with a physics based model of particles, fields, acceleration and energy.

I think one of the basic misunderstanding in the beginning starts with the idea of electric current (a moving electron) as the electrical KE energy media in a circuit. Any simple educational model or analogy must build a foundation that clearly explains that is a confusing simplification of how the circuit works even in a simple battery and lamp circuit. IMO we need a basic fields based approach from the beginning in circuits as explained in books like this.
http://onlinelibrary.wiley.com/doi/10.1002/0471433934.fmatter/pdf

Field phenomena are often felt to be the domain of the physicist. In a sense this is correct. Unfortunately, without a field-based understanding, many electronic processes must remain mysteries. It is not necessary to solve difficult problems to have an appreciation of how things work. It is only necessary to appreciate the fundamentals and understand the true nature of the world.

 

[sophiecentaur]

When I started my education electrons in tubes were still very common so we learned the basic rules of tube operation in a way that was consistent with a physics based model of particles, fields, acceleration and energy.

I think one of the basic misunderstanding in the beginning starts with the idea of electric current (a moving electron) as the electrical KE energy media in a circuit. Any simple educational model or analogy must build a foundation that clearly explains that is a confusing simplification of how the circuit works even in a simple battery and lamp circuit. IMO we need a basic fields based approach from the beginning in circuits as explained in books like this.
http://onlinelibrary.wiley.com/doi/10.1002/0471433934.fmatter/pdf

I think you have missed my point here. That link is not really about "basic" Physics; a lot of it is more advanced than the basics that most people ever grasp. Virtually none of it is needed for the sort of circuit theory and calculations that get cars and computers designed. My Dad explained about Valves and the flow of electrons - whilst they are in a vacuum but he had more sense than to go into solid state behaviour. (I was probably only about 14 at the time). Your point about KE of electrons in a metal is well made. The thing that bothered me most about the triode valve was how the Anode Volts went DOWN when the current went up!
I guess that a lot of the arguments here are based on personal experience. Either people think their education was good or they feel it was 'badly aimed' / just plain bad - depending.

 

[DrDu]

I would not regard the streaming liquid picture to be merely an analogy. After all, the electrons form a liquid, namely the Fermi liquid.

 

[Dale]

The problem is when they don't and end up with a 'mechanical' picture in their minds which is never corrected

That is why I advocate for not giving a mechanical picture at all. Have them address the the concept directly as it is since the analogies are more complicated. I have yet to see ANY alternative model which is simpler than Ohm’s law itself.

 

[sophiecentaur]

That is why I advocate for not giving a mechanical picture at all.

Absolutely fine but have you ever tried to get across a 'non-mechanical' picture to a 12 year old kid of 'average' ability? OR even a class full of them?

simpler than Ohm’s law itself.

That is a Mathematical Model, remember. Mathematical Models are "simple", only for a certain level of ability. You, @Dale are brighter than you imagine if you find Maths is the way to your understanding. But we can all see that - that's not just idle flattery.
It really is a conundrum for education. A vast number of people just don't believe maths.

 

[ZapperZ]

I don't quite understand this discussion now. I thought that the original premise was to find a suitable model to explain to elementary students what is "under the hood"? Ohm's law IS the hood. Just showing the macroscopic relationship between V, I, and R doesn't give you the picture of electrical transport. We can't explain what is presented in Post #1 by teaching the students Ohm's Law!

The Drude Model is the first look under the hood. And if the students or anyone else is more interested in the details, or a more accurate description, then he/she is welcome to look even closer under the hood beyond the Drude Model.

Zz.

 

[sophiecentaur]

I don't quite understand this discussion now. I thought that the original premise was to find a suitable model to explain to elementary students what is "under the hood"? Ohm's law IS the hood. Just showing the macroscopic relationship between V, I, and R doesn't give you the picture of electrical transport. We can't explain what is presented in Post #1 by teaching the students Ohm's Law!

The Drude Model is the first look under the hood. And if the students or anyone else is more interested in the details, or a more accurate description, then he/she is welcome to look even closer under the hood beyond the Drude Model.

Zz.

As I already pointed out, it is a conundrum for education. Nearly everyone who has an opinion has an opinion that is based largely on their personal ability and their experience of their education. This is what is to blame for the path that this thread has taken. But it does demonstrate that a seemingly trivial question has no trivial answer.
You either have to teach the Maths of the situation and tell students to believe in the result and that, later, they will get a better model, or you can try to deliver the mathematical model and it's too hard for them to take so they switch off OR you teach them the mechanical model. The first message of the mechanical model is that the direction of current flow is actually backwards. We know how much that has confused generations who have never got to grips with Vectors and signs.
The only satisfactory path through this one is to make sure that only students who operate at the Formal Cognitive Level should be exposed to anything but the most elementary part of the story about Electricity. Despite the fact that everyone is familiar with Electricity, it is almost as difficult a subject as Quantum Mechanics and we acknowledge that very few people can cope with that one.
So what 'exactly' is electricity??

 

[jim hardy]

Maybe growing up with vacuum tubes makes one lean to 'electron current' since, in our everyday machinery, they are what moves to propagate charge.
Even in solid state devices 'Holes" are unfilled shells in receptor atoms that're locked into the crystal lattice . Those atoms don't move, electrons move between the holes similar to marbles in a game of Chinese Checkers. But technical writers chose to describe the effect as moving positive charge carriers. .

As tubes went away , 'electron current' largely disappeared from the lower level textbooks.

One needs to be fluent in both if he is to survive in industry. US Navy has produced extremely competent people who believe in negative current. My technicians always teased me about "Engineer's Current" , so in the spirit of fun i drew both Engineer's and Secular current as brown and green on my diagrams
old jim

 

[sophiecentaur]

US Navy has produced extremely competent people who believe in negative current.

Ha Ha. Very true. But I would add the words 'in spite of' in that statement.

 

[ZapperZ]

But I don't understand why this issue of people using "negative current" even matters, IF both sides are aware of what is being done. I worked in an electron accelerator, and our "current" are bunches of electrons moving very fast. There is never any confusion when we consider what "current" we are talking about among us.

The problem comes in when someone from the outside who doesn't understand the situation comes looking in, or if both sides are not aware what the other is doing.

Zz.

 

[sophiecentaur]

But I don't understand why this issue of people using "negative current" even matters,

You are probably right in the context that you are working with. But it matters to pretty well every school student learning electricity for the first time and many of them are 'moved on' to the next part of an overloaded Science Course before that have ever grasped it. It's so easy for people who have already got it sorted but even if you try to talk about it to a perfectly well educated adult who's earning many tens of thousands of pounds or dollars per year, you will see the bafflement shutter come down and then we have to talk about something else. Cognitive Dissonance is not good for learning.

The problem comes in when someone from the outside who doesn't understand the situation comes looking in, or if both sides are not aware what the other is doing.

I would say that it is risky (and pointless) to be working a system that's not thoroughly understood by everyone involved. It's bad enough that we often have to deal with metres and feet on the same thread and that's when the units are there in front of our noses.
I have had to deal with electron beam devices on several occasions but I have always managed to put a different hat on when actually in the vacuum. The Anode / Collector Current has always been Positive for me though.

 

[Dale]

Absolutely fine but have you ever tried to get across a 'non-mechanical' picture to a 12 year old kid of 'average' ability? OR even a class full of them?

I would not teach Ohm’s law to 12 year olds at all. I would teach safety, then how to measure voltage and current with a multimeter, and then safety again.

 

[sophiecentaur]

I would not teach Ohm’s law to 12 year olds at all. I would teach safety, then how to measure voltage and current with a multimeter, and then safety again.

I couldn't agree more. The problem is that the Curriculum (all subjects) contains more and more 'items' and each topic has to be taught more and more superficially. In the UK, hardly anything is actually revisited (no time for a healthy spiral curriculum) and many kids only get 2/3 the timetable time for each of Physics, Chemistry and Biology, compared with other 'core' subjects. This is at a time in history when there is more and more Science. In many schools, if you want your kids to take the three subjects 'full time', they need to stay at school longer in the day. Funding is tight and this can't be done for free. (So many woes). What we would probably call basics are omitted until first year at University and that can mean the next three years courses must be squeezed. Meanwhile, University Fees are a massive issue (plus maintenance costs) and kids are being saddled with lifelong loan repayments.
These other issues affect the quality and content of the courses right through Education.
@jim hardy says that practical experience is best. I agree but a practical course will cost twice as much as a paper and pencil course. Many present day teenagers are thinking twice about the whole University thing. Going to hell in a handcart, I fear.

 

[OmCheeto]

I would not teach Ohm’s law to 12 year olds at all. I would teach safety, then how to measure voltage and current with a multimeter, and then safety again.

That's pretty hilarious.
I was just going through my old(1978) Navy electrical instructional manual, and the first chapter was: "How to give mouth to mouth resuscitation."

For the life of me, I can't find my "BEE" notes. "BEE" being the precursor class: "Basic Electrical and Electronics".
I'm guessing I threw all that away, as I'd learned all of that in high school.

ps. Wait a minute... Your post is verbatim topics 1-1 and 1-2. Are you ex-Navy?

 

[Dale]

Your post is verbatim topics 1-1 and 1-2. Are you ex-Navy?

No, I guess I just have the same view of 12 year olds as the Navy has of new Electricians Mates

 

[nsaspook]

For the life of me, I can't find my "BEE" notes. "BEE" being the precursor class: "Basic Electrical and Electronics".
I'm guessing I threw all that away, as I'd learned all of that in high school.

ps. Wait a minute... Your post is verbatim topics 1-1 and 1-2. Are you ex-Navy?

I took BEE in San Diego 32nd street. I decided to challenge the course so I was done in a week. No notes either.

 

[OmCheeto]

I took BEE in San Diego 32nd street. I decided to challenge the course so I was done in a week. No notes either.

hmmm...
scratches head...
"Why did it take me two months?"

Ah ha!

I also took the class in San Diego. And beings that it was December, two months of pretending to be stupid in sunny southern California seemed the logical thing to do.
Next stop: Chicago, in February...


ps. I had a good time there also, in spite of the weather. 10/10 star city, IMHO.

 

[nsaspook]

hmmm...
scratches head...
"Why did it take me two months?"

Ah ha!

I also took the class in San Diego. And beings that it was December, two months of pretending to be stupid in sunny southern California seemed the logical thing to do.
Next stop: Chicago, in February...


ps. I had a good time there also, in spite of the weather. 10/10 star city, IMHO.

I was staying in San Diego for at least another year at schools so I spent the slack time between classes being a good sailor.

 

[Dale]

The problem is that the Curriculum (all subjects) contains more and more 'items' and each topic has to be taught more and more superficially.

So then it seems even more sensible to avoid analogies that are more complicated and of limited applicability. And also advantageous to focus on the thing itself.

 

[sophiecentaur]

Again I agree, in principle. Unfortunately, the requirements for the curriculum are based on over optimistic ideas and the desire of politicians to 'make their mark'. It has been decided that 'everyone' is capable of having (in fact, must have) a thorough appreciation of all modern science. So everything is dealt with but briefly.

 

[jasonRF]

I realize this thread is winding down, but as I read through it I cannot help but recall what Feynman said about modeling the properties of matter. See the beginning of
http://www.feynmanlectures.caltech.edu/I_39.html
B (high school) level students simply are not ready to see even the simplest quantum mechanical explanation of conduction. They will either need to be content with Ohm's law, which they can (and probably should) demonstrate for themselves in the lab, or they can see the Drude model and accept that it will be wrong to some degree. Personally, I don't think I could have handled the Drude model when I was in high school, although a cartoon of the physical picture would have been helpful.

Jason

 

[jcy110]

Conduction and resistance are inversely proportional...conduction being the speed from point a to point b and resistance the roadblocks encountered along the way...

 

[Stavros Kiri]

Conduction and resistance are inversely proportional...conduction being the speed from point a to point b and resistance the roadblocks encountered along the way...

What if someone wants to ruin his car? ...

 

[TedA]

I just wanted everyone to know that I was still here and enjoy reading all this stuff. TedA.

 

[EverGreen1231]

When I was first learning about electricity, I was given more analogies about what it's "like" than any reasonable person could reconcile to the actual phenomena. I've heard all of the references mentioned in the OP and came away more confused than I'd arrived after having heard each. It was only when I confronted the theory head on, without gloves, without "analogies," and without fear that I began to understand. This seems the only correct path.

Electricity is difficult. It's behavior is QM and is not easily understood through intuition. If one wishes to study something that "makes sense," go to mechanical.

 

[ZapperZ]

It was only when I confronted the theory head on, without gloves, without "analogies," and without fear that I began to understand. This seems the only correct path.

What exactly does this mean? What "theory" did you "confronted" head on?

Zz.

 

[EverGreen1231]

What exactly does this mean? What "theory" did you "confronted" head on?

Zz.

Maxwell, circuit theory, etc. I'd thought the analogies were good enough to understand. All they really did was confuse me. Learning the theory was what began to set me straight.

 

[ZapperZ]

Maxwell, circuit theory, etc. I'd thought the analogies were good enough to understand. All they really did was confuse me. Learning the theory was what began to set me straight.

Wait... those theories do NOT explain "conduction" or how charges flow in a solid. So how was that able to "straighten" you out? Are you able to predict the resistivitity versus temperature dependence of a semiconductor, for example?

Zz.