What's the answer?

[Bealman]

I'm curious but I won't ask

[crewearpley40]

Teacher taught newton's theories, bits about hawkings but smoked 20 a day plus had breath that was enough to put people off and i was under 16. Those were the days

[Newportnobby]

I'm amazed/pleased to see the number of replies but it is obvious opinions differ dependent on what/how you were taught or what device you have. A bit like "How do you clean your track?" but with just two possible answers

[Bealman]

There is confusion in all disciplines, because of historical reasons.

A confusing one when teaching physics was electric current. DC current in reality moves from negative to positive, but, it was initially thought to flow positive to negative.

This is important because it determines the direction of electromagnetic fields, and if kids got the current direction wrong, it made the rest of their calculations wrong.

Luckily the examining board at the time in NSW clarified that all exam questions were based on "conventional" current flow.

[njee20]

I think it's more that it's an ambiguously written question, which just means it's inherently open to interpretation. There is no right or wrong, because the way the question is posed is poor. Basically it's something designed to cause debate on the internet. Like this.

[emjaybee]

It's obviously a 'slow-news' week in model railway world.

[Bealman]

Brain food, I guess. A bit like crosswords, even though I have some mates who have PhDs and love 'em.

Perhaps that's why I'm not Dr Bealman 

I HATE crosswords. To me it's like lying on an Australian beach cooking yerself in the sun. You're achieving nothing, made nothing, contributed nothing.

(Heaps of Aussies still do this, by the way)*

There.

I'll bet I've stirred a hornet's nest here 

* As did a young Bealman on arrival on these shores 

[njee20]

Meh, people have different interests. Not sure qualifications are a relevant factor in that. I believe there's more to a PhD than enjoying crossword puzzles...

[Malc]

There is confusion in all disciplines, because of historical reasons.

A confusing one when teaching physics was electric current. DC current in reality moves from negative to positive, but, it was initially thought to flow positive to negative.

This is important because it determines the direction of electromagnetic fields, and if kids got the current direction wrong, it made the rest of their calculations wrong.

Luckily the examining board at the time in NSW clarified that all exam questions were based on "conventional" current flow.

I was taught current direction was opposite to electron flow.

[Bealman]

Yes indeed, Malc. Conventional current. 

The thing I used to hate teaching was Lenz's Law. I still have difficulty getting me head around it.

What was funny though, was supervising exams. You could always tell when the kids got to the electromagnetic questions because they started contorting their hands into funny shapes

[emjaybee]

Ah yes, that takes me back, left hand motor rule, right hand generator rule.

Happy days.

[themadhippy]

right hand generator rule

or geneRIGHTor as drumed into us.
On the subject of selective teaching,why is ohms law  not taught properly, W=VI doesn't work 100% of the time.

[Bealman]

http://www.sengpielaudio.com/FormulaWheel-ElectricalEngineering.htm

BUT....

Real answer is:



Maxwell's equations - not bad for a Scotsman! 

[Train Waiting]

There is confusion in all disciplines, because of historical reasons.

A confusing one when teaching physics was electric current. DC current in reality moves from negative to positive, but, it was initially thought to flow positive to negative.

Very many thanks for this, George.  I have remained at the 'initially' stage until today.  I have wired all the layouts that I've attempted to build on this assumption (apart, of course, for the tracks where trains ran in the 'opposite' direction).
The wiring harnesses on my old motorcycles all start at the positive terminal on the battery.  The negative terminal is attached to the frame.  The frame acts as a sort of common return as we railway modellers understand it.  Presumably, the positive to negative current flow assumption was still current (sorry) when these machines (or their ancestors!) were designed.

Like you, I'm not one for crossword puzzles.  I'd rather have half-an-hour with a good book.

Thanks again and best wishes.

John

[Bealman]

Cheers, John.

To be honest, it doesn't really matter what convention you adopt with DC wiring, as a long as you don't swap over halfway through!

In my head, I've always thought of positive as feed, and negative as return.

As you know, stick a loco on a bit of track, connect wires from a suitable voltage source, and it will go. Swap the wires around, and it gans the other way!

Talking of books, that pic above is from a book called Einstein's Hero's.