How well do introductory students understand an operational definition of electric field?

Operational definitions play an important role in the cumulative, layered structure of physics.  Concepts defined in this way allow the construction of explanatory models that span diverse contexts. Research suggests that introductory physics students struggle to apply an operational definition of an electric field based on the expression E=F/q.  To investigate student reasoning, we administered questions involving simple physical contexts.  In one question, for example, students are asked to explain how the variables E, F, and q are affected when a specific change, such as increasing the charge on a test particle, is made to the context. This talk will analyze selected responses through a dual-process framework, discussing the interplay between intuition and conceptual understanding in student reasoning.