Ampere turn balance (MMF balance) in transformers

[Charles Link]

@jim hardy From what I can tell, the EE's will learn the magnetomotive force concepts for use in transformers as in https://en.wikipedia.org/wiki/Magnetomotive_force, often without ever equating it to a form of Ampere's law for magnetic materials as described in post 29. Meanwhile, in the physics curriculum, they teach a whole bunch about Ampere's law, but the application to the mmf equation often is not presented. Even though I am already retired, my first exposure to the mmf equation was here on Physics Forums about a year ago. It was totally omitted from the electricity and magnetism university coursework that I had. With just a little effort, I was able to show that the mmf equation is a form of Ampere's law.

 

[jim hardy]

I admire and envy your fluency with the equations. I'm a plodder - for me the MMF equation validates Maxwell's .

Yes as you suggest i was taught to sum mmf's just as in KVL we sum EMF's.
I remember Professor writing your simplified MMF equation on the board , i tried it out by working out a couple of simple examples and accepted it. I use it not infrequenty.
Concept of Surface Current was for me just a curious mental trick , necessary for people who use the Maxwell equations so their math will work out. It makes perfect sense though.
If i could measure DC voltage along the surface of a permanent magnet i'd have investigated Maxwell further. (edit i think i actually tried that - i often cross check formulas against observations to refine my meager understanding) Might have an opportunity for further study of Maxwell coming up.

old jim

 

[dlgoff]

View attachment 222192
it was part of an autotransformer based reduced voltage starter

Holy crap; that's a monster. Thanks for the photo.

i can't keep up with @dlgoff for creativity though.

I don't know about that. To me, what's important is having the goodies. ... as you have.
Something I just learned, thanks to you, from investigating magnetomotive force(MMF); the Left-hand Rule to Find North Pole of an Electromagnet:

 

[jim hardy]

Conventional or electron current ?
Now i got to try it...

 

[Charles Link]

Holy crap; that's a monster. Thanks for the photo.

I don't know about that. To me, what's important is having the goodies. ... as you have.
Something I just learned, thanks to you, from investigating magnetomotive force(MMF); the Left-hand Rule to Find North Pole of an Electromagnet:
View attachment 222278

I believe your diagram is incorrect.

 

[cnh1995]

I believe your diagram is incorrect.

I was thinking the same, but seeing Jim's #34, it is electron current and not conventional current. So the right hand rule becomes left hand rule.

 

[dlgoff]

Conventional or electron current ?
Now i got to try it...

electron current

I believe your diagram is incorrect.

Yes. You're right.

I was thinking the same, but seeing Jim's #34, it is electron current and not conventional current. So the right hand rule becomes left hand rule.

Thanks for that.