Title: GR8677.067 Post by: conantee on January 06, 2010, 12:08:00 PM 67. A large isolated system of
![]() ![]() ![]() ![]() ![]() (A) ![]() (B) ![]() (C) ![]() (D) ![]() (E) ![]() Title: Re: GR8677.067 Post by: conantee on October 11, 2010, 12:28:41 PM If you have taken statistical mechanics long time ago, I hope you still remember that
(1) at T=0, all particles goes to ground state energy. (2) particles tend to be at lower energy than higher energy. By this two facts, you can eliminate choices (A), (D) and (E) by reasoning as follows: Since T is greater than some number greater than zero, average energy is not zero since some particles will not be at zero-energy level. (A) is wrong. Next, we can set the upper bound for average energy by saying that the actual average energy is always no greater than the average energy assuming that particles prefer lower energy level and higher energy level equally. This just comes from (2). Well, if particles are equally likely to be in any levels, the average energy is just ![]() The choices for guess are now (B) and (C). Now, you need Boltzmann distribution to pick the right. According to Boltzmann distribution, the number of particles in each level is proportional Boltzmann factor ![]() ![]() If ![]() The correct answer is (C). 22 of 100 people answer correctly. |