Though it may not seem like it, if you’ve seen how much fun I have doing demonstrations - demonstrations are for the student and not for the instructor.
If this simple but inconvenient truth were kept at the forefront of the mind, many of the major crimes of the physics class room would be eliminated. The student in the back row, as well as the student in the front row, should see and hear what is going on. The instructor must examine critically every experiment to be demonstrated with this thought in mind; he should consider the value of an experiment by judging what the student sees and understands rather than by his own personal enjoyment and satisfaction in performing an operation that may be perfectly clear from his vantage point but perfectly invisible to most of the students in his class.
If you have to have a physics degree to understand the experiment, you’re on the wrong track. Likewise, if you can’t see it clearly, you can’t hope to comprehend the action.
After an experiment is set up you may be astonished to see what it looks like from the back of the room. Large scale apparatus, using cameras to magnify the action, clearly visible indicators, and readable charts and drawings are essential. Simplicity (but not crudity) of arrangement and manipulation is paramount. Teachers often avoid simple experiments, favoring those which require elegant and elaborate facilities. By such displays, the student may be impressed and even overawed, but they may in equal parts be being trained that physics happens only in the hallowed halls of the laboratory and through the use of exotic materials - it would also be a mistake to consider that he is better instructed.
The student deserves to see as much of the working arrangement of every experiment as they can understand without being confused by unnecessary detail. It might be stated as a corollary that the experimental arrangement should be more easily understood than the concept that it is designed to illuminate. The foremost purpose of any demonstration experiment is to clarify a physical principle or to show some interesting application of a principle.
If, at the same time, it can amaze and intrigue the student and cause him to do some independent thinking, it more than fulfills its mission. But its primary purpose is not to mystify. Whenever a physics instructor presents a demonstration, they can become a showman; some of the experiments are as clever as any magician’s tricks, and one should make the most of their “show” qualities when appropriate.
Our purpose, however, is very different from any magician’s: the latter makes every effort to conceal and to mystify; the former makes every effort to expose and to clarify the underlying physical principles. Of the many principles taught in elementary physics courses, almost every one is reducible to a mathematical statement that involves three or four symbols only. Yet students constantly stumble over these mathematical expressions which might be made vivid and meaningful if illustrated concretely by simple experiments.
One instructor suggests that a good experiment involves a maximum of manipulation and a minimum of explanation. He goes so far as to suggest giving a demonstration lecture of selected experiments without saying a word! The inspirational value of experiments depends so much upon the manner in which they are presented that the instructor cannot give too much attention to planning his experiments so that they will be given in the proper setting. There is an appropriate time at which to perform an experiment: to show it too soon is to find a class unprepared to appreciate its importance; to delay it by prolonged explanation is to diminish its effectiveness. Thought should be given to exposition, and the lecture should move steadily forward toward some climax. The physics instructor needs to develop a sense of what on the stage is called “timing.‘’