How Transistor works - verifying

[Dmytry]

"children"??
If you really mean children then, apart from saying that a transistor acts a bit like a variable resistor with its value controlled by the third connection, what would be the point of anything more? If you're using terms like "potential barrier" then what sort of children would you expect to be familiar with them?

Frankly, I think that just describing a common base amplifier, and how the signal becomes inverted, would be way too hard for most kids of secondary age (except a few enthusiasts who already have some experience of making up circuits). They may well be impressed with seeing an amplifier actually operate but, as for 'understanding', I doubt it.

What are the circumstances in which you are hoping to present these ideas?

I remember my Dad, in a one-to-one situation, explaining successfully (as I remember) how a thermionic triode works when I was about 11 yrs old. The triode is a much simpler device to describe and, being called a 'valve' it even sounded a bit like a tap.

I recall reading how BJT works in an old book when i was about that age. It was explained that it would normally not pass any current, as two diodes would not, but as the base is so thin, injection of other type of charge carriers into the base by making one of diodes conduct current makes the second diode leak.
It previously explained how diode works with charges being pushed away from midline, and had a drawing of transistor with charges.
Not a very accurate explanation I know, but it made sense to me back then, and is not grossly invalid.

 

[sophiecentaur]

Ummm.
You may feel that such an explanation worked for you but my opinion is that there are many ideas in electronics which are more appropriate and timely for a student to get straight than leaping in with an incomplete model of a very complex device. Let's face it, if they aren't familiar with all the basics then what use is it to have an arm waving model of an object that they may, in fact, never see in their lives as a discrete circuit element?

 

[Dmytry]

Well, I seen it as a real circuit element.

Also, that model is not so bad. It is a common explanation that minority carriers in the base region are responsible for conduction. Of course it does breed misconception with two diodes for some people but I don't recall ever thinking that I can connect two diodes and get this because I knew exactly how 2 diodes work (having learned about rectifier) and the book stressed the bit about carrier injection into thin base. edit: Really, the only difference it had vs the stuff you can hear taught to university students is that this old book didn't define a bunch of terms like "minority carriers" but instead used descriptions of what those are in the text. Which was probably because it was in russian and its easier to be descriptive in this case.

 

[sophiecentaur]

Yes it is a real circuit element and the model only 'creaks' a bit but there aren't many three legged devices seen these days (except for regulators, perhaps). Then again, there are other technologies than the junction transistor.

But in any case, I asked what was meant by "children". Whilst there may be one or two 'nerdy' (no offence) lads in school, teaching a class full of kids of (any) school age about semiconductors in circuits would be way off syllabus and probably a big yawn for them. I say that as a one-time boy-home-constructor. But that was in the 60s. In the last 20 years of teaching, I only came across one student who showed that sort of interest within School and that was only because someone had given him an ancient home constructor kit. He only wanted to do electronics at the 'system level', in any case.

Things have changed recently, at least, in my experience.

 

[Dmytry]

Well the point of education is twofold: teach everyone to read and write and do very basic math, and get started those who will become professionals in complicated fields (who will be few). It would seem to me that west often neglects the second goal nowadays or sacrifices it for the first. Furthermore certain cultural attitudes seem to make it so that only social outcasts become sufficiently invested in technical topics nowadays in the developed countries.
Which is of course helpful for me because otherwise I'd have real trouble competing with the people raised in the western countries who had far more opportunities than I did, and would perhaps have to underbid them instead of being able to set my own price.
I don't really know what you would need to change about the attitudes though. It seems to you self evident that it is important to entertain the majority of students if only minority can benefit from a boring course. It doesn't seem self evident to me. Sure, all the topics beyond basic literacy and numeracy are going to have incredibly small yield, but that small yield is all the highly qualified non-foreign professionals that your country will get.

 

[sophiecentaur]

You are right, in many ways, about the purposes of education. I would say that education is also supposed to 'cultivate' where possible; this is at least as important as teaching basic skills and preparation for a job.
You say "It seems to you self evident that it is important to entertain the majority of students if only minority can benefit from a boring course." but that is not actually true. In the UK we have a National Curriculum which has to be delivered and teachers are answerable if students, their parents, Schools and inspectors are not satisfied with their subsequent exam performance. Of course, many students under-perform because the courses are hopelessly mis-matched to ability and culture for many students. But one has to cover one's arse by making sure that as much of the course content is delivered. If I had been allowed to take classes and deliver material and experiences to them that I deemed 'appropriately interesting' for them, then they would have been a lot less bored and more receptive. That would have been at the expense of following the dreaded Scheme of Work. Teachers who do that will often find themselves being disciplined and told that it is just not their choice.

Our Great Comprehensive Education System is aimed to provide every child with an equal opportunity to do their best in life. That's Motherhood and Apple Pie; one can't argue with it. EXCEPT that it is assumed (and frequently stated) that anyone can do anything if they just get the right education. The National Curriculum is a total One Size Fits All, despite the politicians claiming that it is precisely Not that. Everyone is judged against the standards of everyone else and, thus, half of them will fail to achieve Median Performance (by definition).
Whatever we claim to do in our Schools, LIFE is not comprehensive. Once you leave School or College, you may think that you deserve all the goodies in life but, without indulgent parents, that sort of thing comes to an end. The same thing applies to disabled kids. They may acquire funding for education and care whilst they are minors but many of them find themselves at the bottom of pile for the rest of their lives.
I shall stop my left wing ranting and pirating this thread now! Sorry chaps.

 

[uminair]

here is a video presentation that describes the principle of work of transistor.
http://www.youtube.com/watch?v=fodfowmdfvy&feature=related

nice