Teaching Philosophy (Physics)
First, I want to stress that what is written here is meant to apply specifically to teaching physics majors, rather than those majoring in chemistry, biology or engineering, much less so to teaching physics as part of a liberal arts curriculum. This is not to say that I believe the stated philosophy is not relevant or would be totally wrong in those other instances, but simply that I have a rather narrow objective here.
It is my view that the importance of the classic lecture format for education of professional physicists should not be underestimated. Short of individual or small-group instruction the lecture is the most viable means of communicating the most important element of learning – how to think like a physicist. This includes knowledge of how to approach the problem in an efficient way, how to assess the correctness of the answer by analyzing it in various limits, and the ability to grasp its implications including doing so in the context of other related phenomena, and many other things. Such know-how is not easily transferrable via a concise textbook. I have used peer-instruction and group discussions more or less effectively over the course of my 9-year career as a university physics teacher, but I would not be willing to promote them beyond a supplementary role in the classroom. No one could probably argue that reading a medical textbook and then discussing with your fellow students how to treat a patient under an occasional supervising eye of the instructor is the proper way of becoming a physician. Physics might be different in some respects but not dramatically so. Watching an experienced practitioner performing the process of thinking and applying his knowledge in a particular situation is as important in studying physics as it is in learning medicine or mastering wood-carving. Furthermore, expertise in physics comes no earlier than the student develops intuitive understanding of complicated concepts, or, as Dirac formulated it, the ability to predict the properties of solutions of equations without actually solving them. Developing such intuition is a long process impossible without systematic exposure of students to qualitative ways of analyzing physical situations, such as evaluating characteristic scales, applying dimension analysis, developing an ability to sort different factors by their relative importance, and finally, making a bold simplifying assumption only later to be confirmed (or not!) by the solution of the simplified problem itself. Such “secrets of the trade” are notoriously difficult to communicate in a textbook, and rare (even otherwise excellent) textbooks seriously attempt doing so.
Hold on, but are not students retaining very little from passive listening, while learning much more by actively doing something? This argument is usually made to promote various forms of group discussions in place of a traditional lecture. Well, in my argument for lecturing I do not presume that the classroom time is the only (or even major) time students work on the material. Quite the opposite, a lecture was never supposed to be but a small part of the total studying time. If that practice is not followed the outcome will be a disaster no matter what exactly the classroom time is spent upon -- passive lecturing with no meaningful hands-on practice, or active “doing” after a superficial reading of the textbook prior to the class. I suspect that the perceived “failure” of the lecture might simply be related to the contemporary unwillingness on the part of us instructors to insist on the same commitment from students as used to be the standard in the past. Let us not forget that the lecture-based education somehow coexisted with the remarkable scientific and technological progress for centuries, and who knows, could have been not completely unrelated to it.
Occasional peer instruction is a great way of enlivening a difficult lecture but I would not fathom using this medicine too much. One should be cautious of some side effects. While it is true that below average students are uniformly helped by peer instruction, its benefits for top students are questionable. Such students certainly acquire deeper and clearer understanding of the concepts when they explain those concepts to their lagging peers, but when they are forced to do so very often the law of diminishing returns quickly sets in. Beyond some threshold the time spent instructing peers is the time taken away from learning more advanced things. In my view the reliance on peer instruction is not the right way to train future professional scientists. Also some of the best students often (and correctly) feel that group discussions saddle them with the job the instructor himself is supposed to be doing instead.
Finally, even if it might look like a minor technical issue, I hold strongly that the instructor should refrain completely from using notes during a lecture whenever technically possible. One thing, as aptly pointed by David Griffiths in his Millikan prize acceptance talk, is that reliance of the instructor on the notes breaks that very delicate intellectual trust between the audience and the teacher. The other point might appear counterintuitive. A good lecture does not necessarily equate to a great delivery. Sleek artistic performance often creates an illusion of simplicity which does not serve students well. This is not to say that the lecture must be boring or lousy, but simply that you should not fear embarrassment. There is hardly anything more instructive to a motivated student than seeing her teacher facing a difficult situation, and observing his thought process while (hopefully) successfully resolving the problem. Not having the notes to distract you also makes it easier to pay more attention to the audience and to remain more susceptible to its reactions. It keeps your mind sharper and conditions you better for unexpected questions. If you have never ventured into your classroom without notes, the idea of leaving them on your desk could be as unsettling as riding a two-wheeled bicycle for the first time, but the impact of your teaching can only improve as a result.