Transformers

[WhoTookMyUsername]

Okay, i understand the basic concept of transformers, current induces flux, changing current induces changing flux, changing flux induces current (secondary) once it moves through an iron core.

However i'm confused about quite a few things
1) What property of Iron lends itself to transferring magnetic flux?
2) What are "eddy currents." The way i understand is they are currents that result in energy loss in the magnetic iron core?
3) What is "back EMF"? IS this produced in the iron core or in the primary wire?
4) Why is there no current (ideally) when there is no load across secondary?
5) Why isn't "back EMF" constantly produced to oppose the change in flux?
6) Does some of the "flux" go around the whole core and reach the original primary coil? Would this induce a primary back EMF? If this happens how can current still flow and power be transferred?
Thanks 

[paulsterio]

1) that's a chemistry question rather than a physics question, but it has something to do with magnetic domains and their ability to line up

the rest of your questions regarding eddy currents and back EMF, they require an understanding of the principle of inductance:





in order to understand, which is just far above the VCE course - we can talk about the effects of eddy currents for example, but there's no point because in VCE all transformers are ideal.

[WhoTookMyUsername]

Thanks paul
If there was a question that was like "explain why practical transformers are not ideal (no calculations)" would you say eddy currents in iron core result in loss of energy as heat? or just some electrical energy is converted to heat?

[Phantom-II]

"practical," "ideal"? as in, average quality/size transformers have too much power loss?

agreeing with what paulsterio said, each iron atom is like a small magnet. When you put magnets in mag. field, they line up with the field lines, which then also creates their own field

2) I think because wire is wrapped around metal, both conductors, some current will actually travel out of the wire, into the core and directly to the other end. This causes I in coil lower, so flux is weaker. The eddy currents travel in something like small, circular shapes

3) When you induce EMF through flux or vice versa, the EMF will produce its own flux in the opposite direction. Otherwise electricity would just be generated without some sort of resisting force. The EMF would be in the wire

4)mathematically, V/R=I, no load-> R=0, can not divide by zero. However as R-> approaches 0, I-> approaches infinity? Wait...thats not right...

5)Back EMF implies that it is opposing the flux, so it would be constantly produced?

6) There shouldn't be a back EMF in the primary coil, because the iron core simply carries the flux it is being induced in, as opposed to an example where magnet is inserted to induce flux in coil, which then induces opposite flux and emf. If anything back EMF would be produced in the secondary coil, which then opposes the flux from primary, but isn't strong enough to reverse it.

I'm not 100% about this, we're only near the end of this AoS

[WhoTookMyUsername]

m... does the back EMF occur in the transformer core?
(ideal transformer)

So when there's no load on secondary, the magnetic flux induces an opposing EMF that opposes the AC EMF reducing current to 0 and then P=VI to 0?