See figure attached for questions. Question 1: I would argue that this statement is true. If we think of the equivalent circuit model for a given magnetic circuit the air gap is modeled as a resistor which is a purely linear device. This implies that in the context of magnetic circuits, the airgap is to be thought of as something with linear attributes. Question 2: Electricity is transmitted at high voltages to reduce the energy lost in long distance transmission. Transformers make these high voltages possible, they can step up and step down the voltages as desired. Thus without transformers creating such high voltages, we would have less efficient power transfer over long distances. Question 3: Excitation with sinusoidal voltage implies the presence of a sinusoidal flux. The flux/current relationship on the other hand, will be nonlinear in saturation. As we increase the voltage, the point on the flux/current curve passing through the "knee point" and enters saturation, where the current will exhibit non-linear effects. Theses non-linear effects account for the distortion we are seeing on the output waveform. I had a tough time trying to answer some of these questions, so I'm fairly certain some of the stuff I've said is incorrect or can be better explained. Are my explanations correct? Are only portions of it correct? What would be a better way of answering the question/explaining such a phenomenon? Is there anything else I could mention? I'd love to hear what your answers to the questions above would have been. Thanks again!