Unformatted text preview: Physics 427 – Thermal Physics nd November 19, 2008 2 Midterm Exam ‐‐‐ Part A: Questions ‐‐‐ CLOSED BOOK (Use the 4‐page exam book. Each question is worth 4 points; 20 points total) 1. For a three‐dimensional free‐electron gas, sketch the occupied density of orbitals, D(ε) for T = 0 and T finite. Mark the chemical potential and clearly show if the chemical potential for the T finite case is higher or lower than the T = 0 case. 2. Sketch the P‐V diagram for a Carnot cycle, label the isotherms and isentropes. Label lines and points where the thermodynamic temperature can be defined as τl , or τh , for low, and high, respectively. 3. A perpetual motion machine of the second kind has just two effects: it extracts heat from a reservoir and turns all of it into work. Explain why one should not try to invent such a machine. Be specific. 4. Write down the differential forms of the Helmholtz free energy and the Gibbs free energy and give a real example of a situation where each is useful. 5. Sketch the Helmholtz free energy density of a normal metal, FN, and a metallic superconductor, FS, as a function of applied magnetic field, Ba, from Ba=0 to 50% above the critical field, 1.5Bac. Clearly label FN, FS, and Bac. Please turn in your answers (suggest 15‐20 minutes), and then PICK UP THE OPEN‐BOOK PART OF THE EXAM ...
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- Fall '08
- Physics, Helmholtz free energy