I have read that when the secondary of a transformer has current flow, it will reduce the magnetic flux in the core. This then reduces the back-emf on the primary, causing a increase in current to reestablish the magnetic flux to what it once was. What I want to know is when the secondary produces enough counter flux to decrease the flux in the core to 0, isn't there still magnetic flux in the core? Because the primary creates its own magnetic flux and so does the secondary (even if only briefly because of speed of light delays), they are just opposing each other. It is just like two electromagnets opposing each other. it's like they would each have a little bubble around themselves, except concentrated within the core, lol. The Other question is if the flux in the core is 0 than will the Primary still be able to induce a voltage on the secondary? Normally you would think no because there is no flux for a rate of change to move back through. But if the primary and secondary each still have there own magnetic flux, equally opposing in strength, then a change in the primary's magnetic flux could still move back through the primary's flux and then through the secondary's magnetic flux to still induce a voltage. An analogy could be two bubbles, both are pushing against each other (not popping or combining) and a vibration in one bubble will propagate through the one and into the other bubble. Obviously once the Primary stops changing then no voltage can be induced on the secondary anymore, just like the bubbles, no vibration in one means there can be no vibration in the other(there can but let's say the only possible vibration it could ever have was the one you caused, lol).