1. The problem statement, all variables and given/known data Consider an inductor, with a core of ferromagnetic material, connected to an a.c. power supply. Explain why the contribution of the hysteresis losses to the resistance of the coil is theoretically proportional to the frequency of the oscillator. 3. The attempt at a solution The energy lost per second, i.e. the power, is simply the amount of times the hysteresis loop of the material is 'completed'. So the power used is proportional to the frequency. However, how do I then show from this that the resistance is also proportional to the frequency? It feels like I'm over-simplifying it, but is it simply because I^2 = P/R and since I is not proportional to the frequency, this means R is? I've looked hard, and it may be simple. A text book of mine says to consider representing the hysteresis losses as a resistor in parallel with the inductor - why parallel? I would have assumed the correct approach would be to consider it in series - after all, in a circuit diagram we consider the resistance of an inductor as being placed in series with the inductor.