For our physics class we have to design an experiment investigating the factors affecting an electromagnet's field strength. I have decided to investigate the number of coils in the wire. My only problem is, i'm not sure how to measure the field strength. Our teacher gave us two things which we could use in order to do it: a small compass and a paperclip. People in my class have already suggested the obvious ways: seeing how many clips it picks up, or at what distance a paperclip is affected by the magnet, but our teacher said these ways were not easy to control and that we should keep thinking. I can't think of any other way to use these items in a better way and I really want to know.