Abstract:

The article describes a presentation aiming at addressing students’ misconceptions with regard to essential electrical quantities, more specifically the electric potential (as a basis for understanding the concept of voltage) and the circular frequency. The lecture followed the empirical observation that students, though often using the notion of voltage (relevant to that of electric potential) or the relationship between the frequency and the circular frequency (in the form of ω = 2πf) they do that in a rather procedural manner failing to comprehend the rationale of the concepts and relationships involved.

The lecture started with the notion of the potential in a static electric field and how its definition (as the work associated with a charge’s movement towards a particular position divided by the charge) results in a quantity that, for a conservative field, is solely position-dependent. The students were also motivated to consider the mechanical analogue of the electric potential as the quotient of the dynamic energy of a body (with regard to the earth’s surface) divided by the body’s mass. For an ideal gravitational field (that is, with friction ignored), the obtained quantity (that is the gh product where g is the gravity acceleration and h is the height with regard to the earth’s surface) is also solely position-depended and can be considered as the gravitational analogue to the electric potential. The attention of the students is also drawn on the fact that a positive charge has a similar behavior to a body in the sense that both tend to move from positions with higher to positions with lower potential.

Regarding the frequency f and the circular frequency ω, and the relation ω = 2πf in particular, it was observed that most students would take it for granted without realizing that this specific form is only valid when ω is measured in rad/s. Given that, the students were called on one hand to think what the form of the relationship would be if, for example, the unit of ω was defined as o/s (degrees per second) and on the other hand to justify the relation between ω and f based on logical arguments.

Finally, the association between basic parameters of the circular motion and the sinusoidal variation (such as the period T, the frequency f and the circular frequency ω) is examined which for several students would either go rather unnoticed or would be used without students’ realizing its origin and physical meaning. Apart from the fact that the normal circular motion and the sinusoidal variation are both periodic processes, the explanation focuses on the fact that, while a mobile performs a normal circular motion with period T and circular frequency ω, its horizontal and vertical trajectories form cosine and sine temporal functions with the same period and circular frequency.

The above-described approach was applied in a two-teaching-hour lecture in the framework of the “Electric Circuits I” course at the Electrical & Electronic Engineering Educators Dept., School for Pedagogical & Technological Education (ASPETE), Athens, Greece. It was taken into account that, since the Department’s graduates have the option of working as teachers in technological high schools, conceptual understanding of essential electricity quantities and parameters is essential for them. Following the lecture, a short questionnaire was distributed to the students, that should be answered by means of a 5-grade Likert scale.

Keywords:

Engineering Education, Electrical Engineering Education, electric potential, frequency, circular frequency.