i am having some trouble with understanding the magnetic fields inside transformers and how they relate to back emf.
My first query is: is the magnetic field produced inside the soft iron core aligned with the magnetic field produced in the primary coil, or does it oppose it?
I think it has to oppose the magnetic field in the primary coil by Lenz's law because then the magnetic field in the core would induce a back emf in the primary could which would oppose the primary coil p.d, reducing the current in the primary coil and thus reducing the magnetic field around it so there is a smaller field in the core etc so it will oscillate between decreasing and increasing magnetic field.
However my explanation above does not seem to fit when I consider the secondary coil as being part of a complete circuit and passing current. My text book says that 'when the secondary current is on, the magnetic field it creates is in the opposite direction to the magnetic field of the primary current. In this situation, the back emf in the primary coil is reduced so the primary current is larger than when the secondary current is off', but I am not sure I agree with the first part of that. I would think that the current induced in the secondary could would have to create a magnetic field that would oppose the magnetic field in the iron core by Lenz's law, so that means that both the primary and secondary coils have the same magnetic fields as both are opposing the core magnetic field.
But then when I think about this another way it does not make sense, because then if the secondary could had the same magnetic field as the primary coil, then the magnetic field it would induce in the iron core would oppose the magnetic field of the secondary could even more, and so it would strengthen the magnetic field in the iron core which would cause a greater back emf in the primary could but greater induced emf in the secondary coil so in the secondary coil it would be violating the conservation of energy?
I would be really grateful if someone could clarify which fields align and which oppose each other...