http://www.colorado.edu/physics/phys4230 Most all homework assignments will be due on Wednesdays at 5:00 pm. This first homework is due next Friday (January 23) since next week is a short week. Clicker Question Clicker Question What is the typical relaxation time for a oral medical thermometer? A) B) C) D) E) 1 hour 3 minutes 30 seconds 1 microsecond I thought this was a statistical mechanics class. * Do not worry if you do not have your iClicker today. When you are sitting on them, the wooden and metal toilet seats have different? A: Temperatures B: Energy per particle C: Heat D: Relaxation times E: Some intangible, metaphysical thing Clicker Question A gas at temperature T is mixture of hydrogen and helium gas. Which atoms have more Kinetic Energy (on average)? A: H B: He C: both have same KE Reminders… Reading for next week – Sections 1.6-1.7 Homework #1 due next Friday (January 23) Make sure to start problems early Additional office hours posted on web page Answer: Both have the same average KE 1 Clicker Question Clicker Question How many degrees of freedom in a 1D simple harmonic oscillator? Consider an ideal monatomic gas confined to a plane, that is, 2 dimensions. How many degrees of freedom are there? A: 1 B: 2 C: 3 D: 4 E: Some other number A: 1 B: 2 C: 3 D: 4 E: Some other number Answer: There are 2 d.o.f, one for each of the components of velocity squared in the KE Answer: There are 2 d.o.f: 1 for the KE and one for the PE Clicker Question Clicker Question Consider an ideal diatomic gas at high temperature confined to a plane, that is, 2 dimensions. How many degrees of freedom are there? A gas expands at constant pressure. P P1 V A: 2 B: 3 C: 4 D: 5 E: Some other number V1 V2 Its internal energy U must… A: increase Answer: There are 5 d.o.f.: Two for translation, one for rotation, and two for compression (one KE and one PE). B: decrease C: can’t tell Answer: Since the temperature increases and U is proportional to T, the internal energy must increase as well. Clicker Question A gas can be compressed from a given starting pressure P and volume V by two methods (isothermally or adiabatically). Blue = isotherms Reading for next week – Finish Chapter 1 Homework #1 due today (Friday Jan. 23) at 5 pm Homework #2 due Wednesday, Jan. 28 at 5 pm Pressure Which of the two requires the smallest magnitude of work? A: Isothermal method B: Adiabatic method C: The same work. Reminders… Red = adiabatic Starting Point Answer: A – smallest integral under the curve. Vf Vi Volume 2 Clicker Question For most materials, what is the sign of ∂V ∂T P A: Positive B: Negative C: Positive and Negative both occur frequently Answer: Almost all materials expand when heated (but water does NOT when it is between 0 and 4 deg C); hence the sign mostly positive 3