Thursday, April 16, 2009

What is temperature?

Doug Natelson, writes one of the few blogs on condensed matter physics. He recently wrote a blog on What is temperature? I don't really like his perspective. I think it is best to define temperature in macroscopic and operational terms, using the zeroth law of thermodynamics. The attached slides are from my undergraduate lectures. The key ideas are

* the zeroth law allows us to assign a single number to a thermodynamic system that has the important property that this number will tell us whether or not the system will change when it is brought into thermal contact with another system.

* a thermometer is just a thermodynamic system with just one state variable.

1 comment:

  1. Adkins' "Equilibrium Thermodynamics" ( has a discussion of this view of temperature that I like very much. It is a little dry and formal but also quite rigorous. That said you need some mathematical and physical sophistication to fully appreciate what's going on. I got a lot more out of this book when I first prepared to teach undergrad thermodynamics than when I read it as an undergrad!