Experimentos sobre absorção e emissão de radiação térmica e visível com adaptação do Cubo de Leslie

Abstract

Educational Robotics kits are typically used in experiments on the Newtonian mechanics and for the construction of autonomous robots. Such equipments provide easy access to the programming language for students and teachers. Standard devices are servo motors and touch, ultrasound, light and temperature sensors. The work reported here analyzed the Educational Robotics, namely the integrated data acquisition facility, as a contribution for the study of Modern Physics in the High School, an area that still demands special attention for its effective implementation. Temperature sensors from the LEGO NXT Mindstorms kit were adapted in an experimental set consisting of two Leslie cubes, both made of aluminum and heated by inner incandescent lamps. The first one was a “traditional” cube, presenting two of the outer faces painted in white or black, whereas the other two faces, colorless, were mirror-like polished or abraded. The second prototype was a modified Leslie cube, which inner faces were painted in white and black alternately with respect to the outer faces, also painted with these colors. The temperature sensors, in contact with the cubes outer faces, were connected to the microprocessor and the computer in order to obtain heating plots in real time. The temperature data were collected at 5 Hz for about 1500 seconds, enough to attain heating plateaus. The consistency of results were tested accordingly, especially regarding the paints emissivities, data acquisition time and the equipment fine-tuning. The heating curves showed no significant variations in all the external faces of the traditional Leslie cube. On the other hand, noticeable differences were observed in the modified Leslie cube. The face painted in black in both sides presented the highest temperature, which, after stabilization, were 13 ºC (15 %) higher than the white-white face. This result was ascribed to the absorbance of radiation in the both thermal (infrared) and visible ranges of the electromagnetic spectrum. The system was presented for regular students in the SESI School at Irati – PR, Brazil, which adopts the collaborative learning methodology. The experimental class using this system instigated and raised the students´ interest in the involved physical phenomena, allowing them to discuss advanced themes such as emissivity, thermal balance, electromagnetic spectrum, and black body radiation. In conclusion, experimental designs using automation from educational robotics kits can contribute to the improvement of the Modern Physics teaching and learning in the High School, leading new technologies to the Physics classes.