arXiv subjects

Arturo C. Marti

Publications and source records attributed to Arturo C. Marti.

At least 37 records · Page 2Linked to original sources

arXiv2025

Cause-effect relationships in Maxwell's equations and their implications in the teaching of electromagnetism in introductory physics courses

A thoughtless treatment of Maxwell's equations can lead to the interpretation of the existence of a causal relationship between their different terms and, therefore, that an electric field that varies in time generates a magnetic one and vice versa. In this article we address the problems associated with these interpretations and their consequences for the teaching of physics in introductory university physics courses. First, we develop the main arguments that support that charge and current densities, constant or variable in time, are the generators of electric and magnetic fields. Then, we propose a number of classroom examples at the level of introductory courses that allow us to discuss the reasons why considering the electric and magnetic fields as disjoint entities leads to contradictions. Finally, we analyze their implications in introductory physics teaching.

physics.ed-ph↗

arXiv2024

Understanding student challenges with circulation and Ampère-Maxwell law

We investigated how students apply the concept of circulation when faced with problems related to the Ampere-Maxwell law. For this purpose, we designed a metacognitive pencil-and-paper question, presented it to 65 students, and analysed their responses using phenomenography. We complemented our research by conducting interviews with 12 students. The results show that students tend to think that they can only use the magnetic field circulation to calculate magnetic fields if the curve used is symmetric, and that they do not take into account the shape of the magnetic field lines when applying it. We also find that some students believe that a variable electric field must cross the entire Amperian curve in order to apply Ampére-Maxwell's law and find the magnetic field.

physics.ed-ph↗

arXiv2024

Basin of attraction organization in infinite-dimensional delayed systems: a stochastic basin entropy approach

The Mackey-Glass system is a paradigmatic example of a delayed model whose dynamics is particularly complex due to, among other factors, its multistability involving the coexistence of many periodic and chaotic attractors. The prediction of the long-term dynamics is especially challenging in these systems, where the dimensionality is infinite and initial conditions must be specified as a function in a finite time interval. In this paper we extend the recently proposed basin entropy to randomly sample arbitrarily high-dimensional spaces. By complementing this stochastic approach with the basin fraction of the attractors in the initial conditions space we can understand the structure of the basins of attraction and how they are intermixed. The results reported here allow us to quantify the predictability giving us an idea about the long-term evolution of trajectories as a function of the initial conditions. The tools employed can result very useful in the study of complex systems of infinite dimension.

nlin.CD↗

arXiv2024

Utilizing smartphone sensors for accurate solar irradiance measurement and educational purposes

The global transition towards cleaner and more sustainable energy production is a major challenge. We present an innovative solution by utilizing smartphone light sensors to measure direct normal solar irradiance, the primary component of ground-level solar radiation. We provide comprehensive guidelines for calibrating the sensor using two methods: a professional reference measurement and clear-sky satellite estimates. The latter method is particularly advantageous in resource-constrained environments. Once calibrated, the smartphone becomes a valuable tool for measuring the solar resource. We propose an instructional laboratory focusing on the physics of solar radiation and its interaction with the Earth's atmosphere, exploring solar variations across locations, cloud conditions, and time scales. By integrating irradiance values measured throughout a day the daily irradiation can be estimated. This approach enhances students' understanding of solar radiation attenuation and its relationship with atmospheric interactions. This method offers a practical and educational solution for promoting renewable energy knowledge and addressing the challenges of the energy transition.

physics.ed-ph↗

arXiv2024

Cooling of an objetct by forced convection

We present an experiment on forced convection where a previously heated object is cooled under the effect of a controlled stream of air. We consider a square copper plate in which temperature variations can be considered negligible and we measure the cooling rate as a function of the average velocity of the air stream. We use a thermal camera to measure the temperature field and the cooling curves as a function of time for different conditions. An empirical relation between the characteristic cooling time and the mean velocity of the air stream is reported. The results obtained are discussed in the framework of simple dimensional models and their limits of validity.

physics.ed-ph↗

arXiv2024

Learning difficulties among students when applying Ampère-Maxwell's law and its implications for teaching

We investigate learning difficulties among second-year students on electromagnetism courses when they apply Ampère-Maxwell's law. Using phenomenography, we analysed written answers from 65 undergraduate physics students to four questions on Ampère's and Ampère-Maxwell's laws. We complemented our research by interviewing twelve students. To design the questionnaire, we ran an epistemological analysis of classical electromagnetism which helped us to identify a set of key essential concepts to understand this theory and guided the definition of learning objectives and to draw up the questions. The results revealed that the students found it hard to recognise the validity framework from Ampère's law and to apply Ampère-Maxwell's law. They face particular difficulties to recognise the appearance of the displacement current and the relationship between the circulation of the magnetic field and an electric field that is variable over time.

physics.ed-ph↗

arXiv2024

A home-lab to study uncertainties using smartphone sensors and determine the optimal number of measurements

We present a home-lab experimental activity, successfully proposed to our students during covid19 pandemic, based on \textit{state-of-the-art} technologies to teach error analysis and uncertainties to science and engineering students. In the last decade the appearance of smartphones considerably affected our daily life. Thanks to their built-in sensors, this revolution has impacted in many areas and, in particular, the educational field. Here we show how to use smartphone sensors to teach fundamental concepts for science students such as any measurement is useless unless a confidence interval is specified or how to determine if a result agrees with a model, or to discern a new phenomenon from others already known. We explain how to obtain and analyse experimental fluctuations and discuss in relation with the Gaussian distribution. In another application we show how to determine the optimal number of measurements as a function of the standard error and the digital resolution of a given sensor.

physics.ed-ph↗

arXiv2024

Basin entropy as an indicator of a bifurcation in a time-delayed system

The basin entropy is a measure that quantifies, in a system that has two or more attractors, the predictability of a final state, as a function of the initial conditions. While the basin entropy has been demonstrated on a variety of multistable dynamical systems, to the best of our knowledge, it has not yet been tested in systems with a time delay, whose phase space is infinite dimensional because the initial conditions are functions defined in a time interval $[-τ,0]$, where $τ$ is the delay time. Here we consider a simple time delayed system consisting of a bistable system with a linear delayed feedback term. We show that the basin entropy captures relevant properties of the basins of attraction of the two coexisting attractors. Moreover, we show that the basin entropy can give an indication of the proximity of a Hopf bifurcation, but fails to capture the proximity of a pitchfork bifurcation. Our results suggest that the basin entropy can yield useful insights into the long-term predictability of time delayed systems, which often have coexisting attractors.

nlin.CD↗

arXiv2023

The effect of mechanical degradation on vortex formation and decay in viscoelastic fluids

Transient dynamics in viscoelastic fluids exhibits notable difference with their Newtonian counterpart. In this work we study the changes in the formation and decay of vortex of viscoelastic fluids due to degradation caused by shear stress. With this aim we performed long duration experiments with solutions of polyacrylamide confined between coaxial cylinders. The azimuthal velocity, acquired through digital particle velocimetry, shows oscillations before reaching a steady state. The vortex development is identified by the overshoot, which represents the difference between the maximum velocity and the stationary velocity. Similarly, during the vortex decay, the azimuthal velocity changes direction, and the relevant parameter is the undershoot, representing the maximum velocity of the transient reverse flow. The experimental results show that overshoot and undershoot are closely related to the changes in the viscoelastic properties caused by the mechanical degradation. This effect opens new perspectives in the characterization of the viscoelastic fluids.

physics.flu-dyn↗

arXiv2023

Regular and chaotic phase space fraction in the double pendulum

The double coplanar pendulum is an example of the coexistence of regular and chaotic dynamics for equal energy values but different initial conditions. Regular trajectories predominate for low energies; as the energy is increased, the system passes through values where chaotic trajectories are abundant, and then, increasing the energy further, it is again dominated by regular trajectories. Given that the energetically accessible states are bounded, a relevant question is about the fraction of phase space regular or chaotic trajectories as the energy varies. In this paper, we calculate the relative abundance of chaotic trajectories in phase space, characterizing the trajectories using the maximum Lyapunov exponent, and find that, for low energies, it grows exponentially.

nlin.CD↗

arXiv2023

The Circular Atwood Machine

The Atwood Machine, a classic apparatus in physics education, has historically been pivotal in demonstrating Newtonian mechanics, specifically Newton's Second Law. This study introduces an innovative adaptation, the circular Atwood machine, aimed at exploring circular motion and angular dynamics and integrating emerging technologies, specifically smartphone sensors. Through a rotating disc subjected to controlled external torque, the experiment delves into the relationship between the torque applied and the resulting angular momentum. The study not only presents the theoretical framework but also outlines a practical setup using readily available materials, emphasizing the potential for contemporary technology to enhance the comprehension and teaching of fundamental physical concepts.

physics.ed-ph↗

arXiv2023

Experimenting with RC and RL series circuits using smartphones as signal generators and oscilloscopes

Simple, portable and low-cost experiments as RC and RL series circuits are proposed to experiment with DC circuits. Very common elements are used: a few electronics components (resistors, capacitors, coils and connecting wires) and two smartphones. We consider the charging and discharging of a capacitor in the RC circuit and also that of coil in the RL circuit. Using a smartphone as an oscilloscope we observe voltages variations which are the transient response to a square signal generated in the second smartphone. These voltage variations are directly related to the electrostatic or magnetic energy stored in the circuits. The experimental data have been collected with the smartphone used as an oscilloscope and corroborated with theoretical predictions based on Kirchhoff's laws. The comparison showed differences of the order of the 1\% or less between the calculated capacitance or inductance compared to the manufacturer values. This approach which avoids the use of expensive signal generators, oscilloscopes, or any specialized hardware can be performed in less-favored contexts and even as a home assignment.

physics.ed-ph↗

arXiv2023

Seeing the invisible: convection cells revealed with thermal imaging

Fluid instabilities are ubiquitous phenomena of great theoretical and applied importance. In particular, an intriguing example is the thermocapillary or Bénard-Marangoni instability which occurs when a thin horizontal fluid layer, whose top surface is free, is heated from below. In this phenomenon, after passing a certain temperature difference threshold, the fluid develops a regular pattern, usually hexagonal, of convection cells known as Bénard convection. In general this pattern is not visible to the naked eye unless specific tracers are incorporated into the fluid. The use of thermal imaging is a simple alternative not only for directly observing these phenomenon but also for obtaining valuable quantitative information, such as the relationship between the critical wavelength and the thickness of the fluid layer. Here, we propose an experiment specially suited for laboratory courses in fluid mechanics or nonlinear physics that involves the use of thermal cameras, or appropriate smartphone accessories, to study Bénard convection.

physics.flu-dyn↗

arXiv2023

Semi-collapse of turbulent fountains in stratified media and the mechanisms to control their dynamics

Turbulent fountains are widespread natural phenomena with numerous industrial applications. Extensive research has focused on the temporal evolution and maximum height of these fountains, as well as their dependence on Reynolds and Froude numbers. However, the minimum height of the surrounding ambient fluid, which is removed by the fountain due to the entrainment effect, has received little attention. In this study, we investigate the dependence of this minimum height on the characteristics of the fountain and demonstrate how to control it. Our findings present important implications for technological applications of turbulent fountains, particularly in contaminant withdrawal. We discuss the potential of our results to improve the efficiency of such applications.

physics.flu-dyn↗

arXiv2023

Presentation of the electromagnetic field in introductory physics textbooks and consequences for its teaching

Textbooks play a fundamental role in teaching and learning in school science classrooms. In this paper we investigate the presentation of the nature of the electromagnetic field in a dozen of the world's most popular introductory university physics textbooks. We analyse, from an epistemologically based teaching approach, the didactic treatment of the electromagnetic field in relation to its sources, Maxwell's laws and electromagnetic waves. With this objective, we elaborate a rational reconstruction of the developments that led to the formulation of the nature of the electromagnetic field, Maxwell's laws and their meaning, as well as electromagnetic waves. Next, we formulate criteria based on the key aspects derived from the reconstruction that are useful in the evaluation of electromagnetism textbooks at the introductory level and apply them to the sample of selected books. In light of the results, we reflect on their consequences for teaching. Our analysis indicates the existence of certain inconsistencies in the approach to the electromagnetic field and its relationship with its sources, Maxwell's laws and electromagnetic waves in many of the books analysed.

physics.ed-ph↗

arXiv2023

The sensors of mobile devices: a innovative tool in the teaching of physical sciences

We show how builtin sensors in mobile devices can be used as portable laboratories at the service of teaching experimental sciences, especially physics, in the last years of high school and first years of university. We describe experiments that previously required expensive apparatus or were not feasible in teaching laboratories. Finally, we discuss some perspectives about the use of sensors in the physics teaching.

physics.ed-ph↗

arXiv2022

A home-lab experiment: resonance and sound speed using telescopic vacuum cleaner pipes

We propose a home laboratory in which a telescopic vacuum cleaner pipe and a smartphone are used to investigate sound speed and acoustic resonance. When the pipe is hit or the hands clapped near one end the sound produced is registered by a smartphone. By means of an appropriate application the resonant frequency is obtained. Varying the pipe's length and registering the corresponding resonant frequency allows to obtain the sound speed. This home-lab, first proposed during covid19 pandemic, has been incorporated as a home challenge to experiment with acoustic resonance in new normal times.

physics.ed-ph↗

arXiv2022

Mobile Devices and Sensors for Physics Teaching

This Resource Letter provides a guide to the literature on teaching experimental physics using sensors in tablets, smartphones, and some specialized devices. After a general discussion of the hardware (sensors) and the software (apps), we present resources for experiments using mobile-device sensors in many areas of physics education: mechanics, oscillations and waves, optics, electromagnetism, matter, modern physics, and astronomy.

physics.ed-ph↗