Warm-Up Exercise 13

Due 12:15 pm, Wed 26 Sep 2012

Physics 123, Fall 2012

Reading assignment: 22.8, especially the marble example but not the “Adiabatic Free Expansion: One Last Time” example. Also: “What is entropy?” handout posted to website, through Example 1.

Using ideas from both the reading and from the last lecture, explain why heat flows from hot to cold when the process of energy exchange between two objects is "random". (How can you get directed motion of heat, when energy is being exchanged both ways?!)

We learned last lecture that entropy always tends to increase. However, when two systems A and B can exchange energy, the entropy of system A always decreases when system A gives energy to system B. If that's so, why would energy ever spontaneously flow from system A to system B? (It often will. When? Why?)

 In the "What is entropy?" handout, what was significant about the equation dS1/dE1 = dS2/dE2?