Physics final exam question: kelvins versus Celsius degrees

Physics 205A Final Exam, Spring Semester 2009
Cuesta College, San Luis Obispo, CA

Cf. Giambattista/Richardson/Richardson, Physics, 2/e, Conceptual Question 13.3

[10 points.] Are there any special circumstances that kelvins or Celsius degrees can be used interchangeably? Explain your answer using the properties of heat and temperature.

Solution and grading rubric:

• p = 10/10:
  Correct. Kelvins or Celsius degrees can be used interchangeably if changes in temperatures (delta(T)) are involved, typically in calculating the thermal expansion of materials, or the heat transferred to/from thermal energy systems. Discusses/demonstrates the distinction between temperature and temperature differences.
  
• r = 8/10:
  As (p), but argument indirectly, weakly, or only by definition supports the statement to be proven, or has minor inconsistencies or loopholes.
  
• t = 6/10:
  Nearly correct, but argument has conceptual errors, or is incomplete. Understands the distinction between kelvins and Celsius degrees only.
  
• v = 4/10:
  Limited relevant discussion of supporting evidence of at least some merit, but in an inconsistent or unclear manner.
  
• x = 2/10:
  Implementation/application of ideas, but credit given for effort rather than merit.
  
• y = 1/10:
  Irrelevant discussion/effectively blank.
  
• z = 0/10:
  Blank.
  

Grading distribution:
Sections 30880, 30881
p: 32 students
r: 0 students
t: 6 students
v: 0 students
x: 1 student
y: 0 students
z: 0 students

A sample of a "p" response (from student 1991):

Another sample of a "p" response (from student 0402):

Another sample of a "p" response (from student 1141):

A sample of a "t" response (from student 2484):