Abstract
Understanding how students reason about electromagnetic waves (EMWs) remains a challenge in physics education. Rather than viewing student thinking as dominated by stable misconceptions, this study adopts a resources-oriented viewpoint to examine how students activate different conceptual ideas across contexts. Written responses from 37 students to five open-ended questions about EMWs were analyzed, with each answer treated as a student question unit. Through inductive coding, seven conceptual resources were found, including medium interaction reasoning, constancy of EMW speed reasoning, field-based wave generation, energy transfer to matter, and self-propagation in vacuum. A descriptive frequency analysis discovered strong context dependence on resource activation. Different resources consistently dominated different questions, with minimal overlap across contexts. Medium based reasoning was most prominent when comparing wave speeds in different materials, field-based reasoning dominated explanations of wave generation, energy-transfer reasoning dominated microwave-heating explanations, and vacuum-propagation reasoning dominated questions about spread in empty space. These patterns were recurring across many student responses. The findings show that students possess a repertoire of productive conceptual resources that are selectively activated rather than uniformly applied. This study stresses the importance of instructional approaches that support the coordination and refinement of students’ existing ideas across contexts.