Determinação do equivalente mecânico do calor através de medidas elétricas

Abstract

Scientific experimentation is a practical activity that can be widely used in the classroom to boost the motivation of students for learning Physics concepts. It can also be promising to improve the relationship between teacher and students. Experimentation can be used as a complementary methodology for the theoretical classes of Physics in order to facilitate the understanding of physical concepts usually treated in an abstract and mathematical way. Experimentation can be applied as a demonstration activity, in which the teacher is the mediator of the activity, or an activity performed by the students themselves, aiming the description of a investigated phenomenon. In this work we perform an experiment for the determination of the mechanical equivalent of the calorie through a different approach to the celebrated experiment carried out by James Prescott Joule. Our goal was to introduce new technologies and devices used to monitor the physical properties of the system for obtaining the equivalent between joules and calories through measurements of parameters such as electric voltage and current. Using a solar photovoltaic cell, as a power source, connected to a resistor inserted in an adiabatic calorimeter, we explore concepts such as heat and temperature and the difference between both, energy, analysis and processes of thermodynamic systems, the laws of thermodynamics and the Joule and photovoltaic effects. Our proposal was successfully received by the students, having a motivating and integrative character. It is also promising for the mathematical treatment of the phenomena described through propagation of errors, by plotting and fitting the curve obtained experimentally and the modeling of the system. Our educational product consists of a guide for assembling the experiment and several suggestions of physical concepts that can be approached during the execution of the experiment in a simple and adequate language for high school Physics teachers.