Students' reasoning in analyzing temperature from P-V diagram representing unfamiliar thermodynamics process

Abstract

Thermodynamic processes discussed in textbooks are typically presented in the P-V diagram and limited to familiar processes such as isobaric, isochoric, isothermal, and adiabatic. The purpose of this qualitative research was to explore students' reasoning in analyzing temperature from given P-V diagram representing thermodynamics processes that do not belong to one of those familiar processes. We interviewed 6 students as the volunteers. The interview was guided by two P-V diagrams. First, students dealt with a process that was similar to but different from isothermal or adiabatic. Second, students dealt with a process which the pressure decreased linearly with volume. We also asked the students to convert the P-V diagram into the T-V diagram. We found that the students tended to use the surface features of the diagrams, instead of applying PV=nRT appropriately. For example, they tended to think of a curved P-V diagram as an isothermal or adiabatic process, and in interpreting a linear P-V diagram they tended to think temperature must be constant if the pressure decreases linearly with volume. The students also failed to convert the P-V diagram to the T-V diagram due to the lack of idea and mathematical skill to solve the problem.