Vortex electric field (VEF) is one of the difficulties in the course of “Electromagnetics”. Although the loop integration and curl can accurately describe its differences from the electro-static fields (ESF), the unglamorous mathematical formulas cannot help students to understand their physical essence. Walter Lewins demonstration experiment on voltage measurement in a VEF intuitively presents the difference between VEF and ESF, but it also brings many doubts to students. This article discusses the distribution of electric field and charge accumulation in a conductor circuit in a VEF under equilibrium, and answers the question of what the “voltage” measured in a VEF is. These analyses are beneficial for deepening students understanding of the concept of VEF and its differences from ESF, while it also cultivates the scientific spirit of seeking the essence through phenomena.
