A good example that shows that the magnetic flux must extrude out side of the core in order to produce an EMF in the secondary,as the conducting wire is around the outside of the core,and not within the core where the magnetic flux is said to be contained. If a transformer is said to be 90% efficient,then 90% of the magnetic flux induced by the primary coil must be cutting the secondary coil.

A number of posts back, I asked this question:

"And whenever there is a changing magnetic field, there is also a corresponding changing ______ field."

To help with your question, perhaps you or Mags could try filling in the blank. (Also, see this post above)

Really?

Quote faradays law: Any change in the magnetic environment of a coil of wire will cause a voltage (emf) to be "induced"(not electrical environment) in the coil. No matter how the change is produced, the voltage will be generated. The change could be produced by changing the magnetic field strength, moving a magnet toward or away from the coil, moving the coil into or out of the magnetic field, rotating the coil relative to the magnet, etc.

So the change in magnetic field strength(and thus magnetic flux) causes an EMF to be produced in a coil(loop) of conducting wire.

Enjoy.

https://www.youtube.com/watch?v=x-EuPGl8JjE

@Tinman - You have your theory here, that's fine. I merely am trying to point out which has been studied and found over the course of some 184 Years of experiments.

Faraday in 1834 discovered Induction and formulated his works around what he found. He was right... Then Maxwell came along and changed it all around a bit, to include some more cool stuff... Then, sadly, Heavyside came along and destroyed it all... taking out all the cool stuff and leaving layman textbook rubbish...

I have tried to give you perhaps the best information on the subject of Induction to date: George I Cohn - Electromagnetic Induction - Below again for download.

It is well known, there are Two Types of Induction:

1: Flux Linking (emf = -NdPhi/dt) - Typically Transformer Induction See: (Magnetic A Vector Potential)
2: Flux Cutting (emf = Bvl)          - Flux Cutting

Both are different forms of Induction, both Induce a Magnetomotive Force in a Conductor that is correctly situated.

So, you're not wrong, I am not saying that, all I am saying, is that the method you describe is not currently considered correct when it comes to Transformer Theory. Transformers work on the Flux Linking Laws, not Flux Cutting, the Homopolar Generator works on the Flux Cutting Law. Also, the Velocity (v) of the Conductor with a Length (l) moving at Right Angles to the Magnetic Field (B) is Flux Cutting.

Thanks for the Video, I did enjoy.

   Chris Sykes
       hyiq.org

P.S: Richard Feynman says the same thing, "Together the two Laws, the two Effects, form one beautiful rule..." See below Audio file: Feynman Quotes - Motion Of a Magnet Electric Field Generated weather or not conductor present - Also see: Feynman_Physics_Lectures_Vol2_Ch_15_Vector_Potential.pdf

...

Isn't it ironic. We had access to Electricity before we had induction... Some 184 years after Induction was discovered, we here debate its principals...

One of my favorite documentaries: Shock And Awe The Story Of Electricity - / 2:54:54 so leave plenty of time...

   Chris Sykes
       hyiq.org

Not sure I understand this after all. I don't see how the diode helps if it sends current the wrong way as shown by the green arrow. We want current to keep flowing in the red arrow direction so we some how need it to follow the purple arrow path that shows it being fed back into the coil in the same direction the initial red arrow current was going.

@gotoluc- As simple as it is, can you make a schematic of your diode circuit and the direction "electron" current flows in it?

In the pic below,the red arrows show conventional current flow direction when a current is supplied by a power source to the coil. The red + and - show the voltage polarity. The blue arrows show the current flow direction when the supply current to the coil is broken,and the blue + and - show the voltage polarity. So you see,the current will continue to flow in the same direction when the current supply to the inductor(coil) is broken(disconnected),but the voltage polarity will invert.

I was waiting for your comment on this one Brad as Jeg is using AC, switching coil connections and not showing how the input power is affected while doing these changes. So I didn't understand how it could compared to your original test suggestion?... but I'm always eager to learn something new

Hopefully Jeg can do the bulb load and show how it affects the input power

Luc

Jeg is showing something different,and indeed his power draw will go up when the secondary has a load placed on it. But i like what he showed,and i wonder who here knows why the two coils repel when hooked up one way,and yet attract when they are hooked up the other way.
here is a little hint-->note the size and shape of each coil.

So let's go back to my drawing again. Let's assume an alternating (or varying) current is applied to the primary. An associated flux is produced within the high permeability core as shown by the two arrows. Will we see an emf produced on the wires of the secondary? If not, why?

Yes you will see an EMF produced on the wires of the secondary,as all the magnetic flux is not confined within the core.

Let's assume for a moment that the core has a very high permeability and all the varying flux is retained within the core. Will there be an emf on the secondary? If not, why?

No,there will be no EMF on the secondary,as all the magnetic flux is retained in the core.