So I did an experiment a this week on the relationship between two tightly wrapped coils with same length and number of coils in a transformer. This was in a compete circuit using AC currents. I measured the Voltage, keeping the currents the same. One experiment had an iron core between the two coils and I varied the distance between the two coils and got a linear relationship. When I used an air core, the relationship between distance and voltage became and inverse function. I don't understand why.