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Originally Posted by jambutty
Which reminds me. Before anyone asks I think that I had better explain back EMF.
When a Direct Current is passed along a wire it creates a magnetic field around it. If another wire is passed through that magnetic field a current is induced in that wire. The same applies to an Alternating Current except that the magnetic field also alternates in that in one instant there is no magnetic field and one two hundredth of a second later it rise exponentially to maximum and in the next two hundredth of a second it falls exponentially back to no magnetic field and continues thus.
Whether the wire is moved through a magnetic field or the magnetic field is moved through the wire makes no difference, a current of lower value is still generated in that wire but it is 180 degrees out of phase with the original. However the wire carrying the initial current is also subject to the changing magnetic field and an opposite polarity current is generated in it. This current opposes and cancels out some of the original current.
So as an example, and please don’t take these figures literally, it is just an example to establish the principle. If a wire is carrying an alternating current of say 10 amps and it has a back EMF of 1 amp induced in it the overall effect is that only 9 amps flow. So to ensure that there are 10 amps available something like 11 amps would need to be generated at source. Thus the back EMF creates losses.
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I don't think anyone would have asked.
You forgot to mention eddy currents (higher losses due to them which is why a solid iron core isn't used in A.F. and power transformers) ,
Off the top of my head I seem to remember that if the current was at 180 degrees it would actually cancel itself out therefore transformers would be of no practical use at all, but before we get bogged down in techno waffle and have to talk about phase shifts and vectors, that is only going to confuse and should not be used to baffle but always on a non technichal site such as this be put in it's simplest of terms.