Identifying Student Difficulties with Entropy, Heat Engines, and the Carnot Cycle

TL;DR

This study investigates upper-division students' misconceptions about the Second Law of Thermodynamics, heat engines, and the Carnot cycle, revealing persistent difficulties in understanding and reasoning about thermodynamic concepts.

Contribution

It identifies specific student misconceptions in thermodynamics, highlighting the complexity of teaching heat engines and the Carnot cycle at the upper-division level.

Findings

Students struggle to connect the Carnot cycle with the Second Law.

Students have difficulty reasoning about physically impossible situations.

Misunderstandings include differentiating between differential and net changes.

Abstract

We report on several specific student difficulties regarding the Second Law of Thermodynamics in the context of heat engines within upper-division undergraduates thermal physics courses. Data come from ungraded written surveys, graded homework assignments, and videotaped classroom observations of tutorial activities. Written data show that students in these courses do not clearly articulate the connection between the Carnot cycle and the Second Law after lecture instruction. This result is consistent both within and across student populations. Observation data provide evidence for myriad difficulties related to entropy and heat engines, including students' struggles in reasoning about situations that are physically impossible and failures to differentiate between differential and net changes of state properties of a system. Results herein may be seen as the application of previously documented difficulties in the context of heat engines, but others are novel and emphasize the subtle and complex nature of cyclic processes and heat engines, which are central to the teaching and learning of thermodynamics and its applications. Moreover, the sophistication of these difficulties is indicative of the more advanced thinking required of students at the upper division, whose developing knowledge and understanding give rise to questions and struggles that are inaccessible to novices.