Experiments in Physics Instruction

24 Jan 2012


We propose that in the history of physics most of classical experiments fall into one of three groups: observational experiments, testing theoretical model experiments, and application experiments. Initial observational experiments occur when physicists study an unknown phenomenon, they help develop a new model. For example observations of the behavior of gases in the 17th century, observations of the spectra of gases in the 19th century, or Becquerels observations of a photographic paper wrapped around uranium-laden cross. Before physicists conducted these experiments, they could not make theoretical predictions of what was going to happen.
Testing experiments are usually conducted to test or disprove a certain hypothesis, idea, or a prediction. For example Hertz’s experiments tested Maxwell’s predictions of electromagnetic waves. The Stern-Gerlach experiment tested the idea of space quantization. Physicists performing these experiments could use a theoretical model to make a prediction about what they expected to observe if their model was correct. Application experiments utilize and synthesize physics concepts developed and tested earlier, for example planning a satellite exploration of a comet or designing a method to detect blood glucose.

Experiments in traditional physics instruction are used as lecture and high school classroom demonstrations and as laboratory experiments. There are two pedagogical techniques used for lecture demonstrations. In a traditional course students observe an experiment and then the instructor explains what happened and why. In reformed instruction students predict what is going to happen before the experiment, and then reconcile their predictions with the observations that follow. The latter has proven to be more effective that the former. Students make predictions using their nave conceptions and then modify these conceptions based on the outcome of the experiments. Traditional laboratory experiments usually have as a goal to verify a principle or a concept that the students already learned from the instructor. The emphasis is on quantitative analysis of data with a great deal of guidance on how to execute the experiment. The theory is often provided with the laboratory instructions.
In some non-traditional introductory physics courses such as Workshop Physics, experiments play a different role. Students make observations and invent a concept that explains them. This approach is much closer to the practice of real practice.
We suggest that this method can be taken father. We propose that all physics experiments
used in instruction can be classified according to the goal of the experiment :
1) Observational experiment. The goal is to observe a new phenomenon. Students later devise explanations for the observations.
2) Testing experiment. The goal is to test whether the explanation devised for some observed phenomenon works. Students use explanations that they constructed to explain some type 1) experiment to predict an outcome of a new experiment.
3). Application experiment. The goal is to apply the explanation that has been tested in 2) to explain new phenomena or design technical devices.
Using different pedagogical treatments for these types of experiments, instructor can teach the students to differentiate between observational evidence and inferences. Students learn to test inferences experimentally and see the applicability of their ideas. They acquire science process skills. This purpose of this paper is to encourage instructors change the approach to the experiments that they already use in lectures or laboratories without adding any new activities.

Qualitative applications

1. Show a demonstration to the students, ask them to explain it using a concept that was tested before, and decide how they will test their explanation. Example: A candle is lit on a plate with a small layer of water and then covered with a glass jar. Students observe that after a short time, the candle goes out and water goes into the jar.
2. Ask the students to predict the results of a demonstration before they see it using a concept that they have tested before and then reconcile their prediction with the actual experiment. Example: An enclosed box on wheels with a floating helium balloon on a thread attached to the bottom of the box, is made of clear plastic. The students predict what will happen if the box is pushed abruptly (the balloon moves in the direction of the push).
3. Perform a demonstration. Ask students to predict what will happen if some parameter in the experiment is changed using the concepts that they have constructed before. Example: Students observe 45 W and 60 W light bulbs connected in parallel to an outlet (a 45 W bulb is less bright). Then they need to predict which bulb will be brighter if they are connected in series.
Quantitative Applications
1. Students design an experiment to answer a question. For example: how would you determine if a material is an electrical conductor or a non-conductor?

2. Students design a measuring instrument (or a method) and indicate the limits of its measuring ability. An example can be to design a method to measure the mass of an object on a space station orbiting the Earth.
3. Students make a prediction so that something occurs successfully on the first try. For example they need to deflect the electron beam of a cathode ray tube to a selected location using a combination of magnets with known poles.

References: Role of experiments in physics instruction a process approach, E. Etkina, A. Van Heuvelen, D.T. Brookes, D. Mills

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