My physics instructor in college didn't answer any questions like that. He barely lectured, in point of fact. He gave us a mountain of assignments, chosen by selecting from the state database of Physics problems by the criteria of being in the top X% (I don't recall the exact number; I'm inclined to think 5) of questions gotten wrong; many of the problems were -way- beyond the scope of the book we were nominally learning from. It took me longer to complete two weeks' worth of assignments than it took me to do the homework for every other class throughout the entire semester, including research papers.

That was the whole of the class. It was the most effective class I have ever taken. There were a few problems where the state database had the wrong formula for calculating solutions (which explains how -they- got into the "hardest problem" set; nobody could ever get them right); I remember one in particular was off by a multiplicative factor of 4pi. Those were quite possibly the absolute best learning experiences; not only did you have to solve the problem, you had to -understand- it, on a very deep level, in order to first realize that they, not you, are wrong, and then figure out exactly why their solution was wrong.