Abstract:

Many properties of light have represented a major challenge to humanity for centuries. Aristotle and Descartes believed that its speed was infinite until the second half of the 17th century, when the first experimental determinations were carried out. The speed of light in vacuum is a universal constant with an exact value of 299792458 m/s in the International System of Units. In air, its value is slightly lower, and this speed does not depend on the reference frame in which it is measured.

Competence-based education is oriented towards an evaluation model linked to student training, promoting the development of skills to identify and solve problems and to make informed decisions. In this framework, active methodologies such as Project-Based Learning (PBL) and flipped classroom approaches play a key role, as they place students at the center of the learning process and encourage autonomy, critical thinking, and collaborative work. Rubrics for competency assessment have emerged as an effective tool for collecting evidence of learning and for evaluating not only conceptual understanding but also procedural and attitudinal skills.

In this work, we present a proposal for a rubric to evaluate competencies in a Physics laboratory practice in which the speed of light is determined indirectly. The activity is designed as an integrative task in which students must connect theoretical concepts with experimental procedures and data analysis.

First, the electrical permittivity of the vacuum is obtained by measuring the capacitance of a parallel-plate capacitor while varying the distance between its plates, using a capacitance meter. From the experimental data, a linear relationship is established, and its slope is determined through a least squares fit, allowing the estimation of this quantity. Students are required not only to perform measurements but also to justify their experimental design and assess possible sources of uncertainty.

Next, the magnetic permeability of the vacuum is obtained using a solenoid through which different electric currents are applied. The magnetic field at the center of the solenoid is measured using the magnetic sensor of a smartphone. Again, a linear relationship is obtained from the experimental data, and the slope of this relationship is determined through a least squares fit. This stage emphasizes the use of low-cost instrumentation and the critical interpretation of sensor limitations.

Finally, once both the electrical permittivity of the vacuum and the magnetic permeability of the vacuum have been determined, the speed of light is calculated from their relationship, including the corresponding absolute and relative uncertainties. The proposed rubric evaluates multiple dimensions, including experimental design, data analysis, error treatment, interpretation of results, and scientific communication. In addition, it provides transparent assessment criteria that help students understand expectations and improve their performance.

Keywords:

Competence-based approach, rubric, teaching-learning, speed of light.