In this work, we propose an inexpensive laboratory practice for an introductory physics course laboratory for any grade of science and engineering study. This practice was very well received by our students, where a smartphone (iOS, Android, or Windows) is used together with mini magnets (similar to those used on refrigerator doors), a 20 cm long school rule, a paper, and a free application (app) that needs to be downloaded and installed that measures magnetic fields using the smartphone’s magnetic field sensor or magnetometer. The apps we have used are: Magnetometer (iOS), Magnetometer Metal Detector, and Physics Toolbox Magnetometer (Android). Nothing else is needed. Cost of this practice: free. The main purpose of the practice is that students determine the dependence of the component x of the magnetic field produced by different magnets (including ring magnets and sphere magnets). We obtained that the dependency of the magnetic field with the distance is of the form x ^–3 , in total agreement with the theoretical analysis. The secondary objective is to apply the technique of least squares fit to obtain this exponent and the magnetic moment of the magnets, with the corresponding absolute error.

In recent years, personal exposure to Radiofrequency Electromagnetic Fields (RF-EMF) has substantially increased, and most studies about RF-EMF with volunteers have been developed in Europe. To the best of our knowledge, this is the first study carried out in Mexico with personal exposimeters. The main objective was to measure personal exposure to RF-EMF from Wireless Fidelity or wireless Internet connection (Wi-Fi) frequency bands in Tamazunchale, San Luis Potosi, Mexico, to compare results with maximum levels permitted by international recommendations and to find if there are differences in the microenvironments subject to measurements. The study was conducted with 63 volunteers in different microenvironments: home, workplace, outside, schools, travel, and shopping. The mean minimum values registered were 146.5 μW/m² in travel from the Wi-Fi 2G band and 116.8 μW/m² at home from the Wi-Fi 5G band, and the maximum values registered were 499.7 μW/m² and 264.9 μW/m² at the workplace for the Wi-Fi 2G band and the Wi-Fi 5G band, respectively. In addition, by time period and type of day, minimum values were registered at nighttime, these values being 129.4 μW/m² and 93.9 μW/m², and maximum values were registered in the daytime, these values being 303.1 μW/m² and 168.3 μW/m² for the Wi-Fi 2G and Wi-Fi 5G bands, respectively. In no case, values exceeded limits established by the International Commission on Non-Ionizing Radiation Protection (ICNIRP). Of the study participants (n = 63), a subgroup (n = 35) answered a survey on risk perception. According to these results, the Tamazunchale (Mexico) population is worried about this situation in comparison with several European cities; however, the risk perception changes when they are informed about the results for the study.

We believe that a natural focus of the physics education research community is on understanding and improving students’ learning in our physics courses. Due to the increase in technology, we can bring laboratory experiments closer to our students. It is necessary to update our laboratories technologically to get closer to the world in which our students live. With this in mind, we have considered the magnetic field created by a linear quadrupole and we have studied its dependence on distance, n being the exponent of distance. The main objective of this exercise is for our students to discover that the exponent n is very close to –4. The purpose of this work is to show that a laboratory is a powerful tool that increases significant learning under three conditions: 1) the practice must not be too sophisticated; 2) students must handle objects in the lab; and 3) the practice must be scientifically accurate, including the fitting using the least-squares approximation, and the following and necessary error calculation. We provide this practice so that all interested physics teachers can use it and adapt it to their specific laboratory.

The objective of the present study was to evaluate the use of powder made out of Roselle Calyx Wastes (RCP) in developing a biscuit formulation with acceptable sensory value. Roselle calyxes were infused in water in a 1:10 ratio. The residual infused calyxes were dried at 50 °C for 16 h, grounded, sieved through a 50 mesh, and stored in plastic bags until used. The biscuit formulations were enriched with RCP at 0% (BC), 5% (BRCP5), 10% (BRCP10), and 15% (BRCP15). The amount of RCP added to the biscuit formulation did not change the protein content. However, the addition of RCP significantly affected the biscuit’s color; the lightness parameter (L*) decreased as the RP content increased from 69.66 to 49.04. The sensory evaluation showed that the control biscuit and the biscuit enriched with 5% of RP were the best accepted. As for the antiradical activity, the formulation with the highest activity was presented by the BRCP15 (587.43 µmol Trolox/100 g dwb). On the other hand, BRCP5 presented 189.96 µmol Trolox/100 g dwb. Therefore, the biscuit formulation with RCP at a 15% enrichment could be used to commercialize a functional product.

Cocoa bean shell (CBS) is one of the main by-products of the cocoa processing industry and represents about 20% of the bean. This product has been suggested as a food ingredient due to its aroma, high dietary fiber, and polyphenol contents. This work shows the effect of grinding degree (GD) and grinding method on the physicochemical characteristics, total phenolic content (TPC), and antioxidant activity of an aqueous infusion of CBS. Three particle sizes of CBS powder and two milling methods (mechanical and electrical) were used to prepare a hot water infusion. The infusions presented a pH in the range of 5.37–5.80. In both husks and independently of the GD and the grinding method, the TPC was higher than 141 mg of gallic acid equivalent per g (GAE/g), an antioxidant activity greater than 304 µg of Trolox equivalent per g (µgTE/g). The results indicate that CBS can be an excellent alternative for the design of biofunctional beverages, giving added value to this agro-industrial residue of southeastern México.