Open-circuit voltage

Voltage in the context of electric circuits is a quantity that can be associated with any (ordered) pair of points. It is defined as the amount of work done on a charge by the electric field in the circuit while it is moved from the first point to the second. Even for two points in a circuit that are not directly connected by a circuit element (i.e., an open circuit), a voltage can be defined. A switch that has been opened is a particular instance of an open circuit.

The voltage in open circuits has been the focus of a decoding interview as well as of extensive research on student understanding (within Physics Education Research and Engineering Education Research).

Decoding work done

Identification of bottleneck

The voltage in an open circuit is a difficult concept for many students in electrical engineering or physics courses. Often, this difficulty occurs first when voltages across open switches are considered. As there is no direct conducting path between the two terminals ("ends") of the open circuit, and hence no current flows between the two points across the open circuit, it is difficult for students to grasp that (1) the concept of a voltage still applies and (2) this voltage may have (and in most meaningful cases has) a value other than zero.

Related scholarly work on this bottleneck

Student understanding of the voltage across an open circuit (or across an open switch) has been the focus of several studies in Physics and Engineering Education Research. Much of this work has been summarized in a review article by Timmermann and Kautz presented at the Research in Engineering Education Symposium in Dublin in 2015.

References

Timmermann, D., and Kautz, C.; Student understanding of open switches and open circuits: What do we (not) know?, In Research in Engineering Education Symposium 2015 (REES2015). Dublin, Ireland (2015).