Quiz 2 Solution notes

Detailed, down-loadable solutions to the quiz are posted above. This is a less technical, conceptual solution guide and discussion which should be complementary to that:

1) "kinetic energy". Acually you should say " average kinetic energy of the individual atoms and/or molecules of the gas". +1 for mentioning "average" or "molecules"...
If you mentioned pressure, sorry, that has nothing to do with this class. Conceptual physics is about understanding seeing the connection between a familiar macroscopic property (temperature) and a the microscopic (atomic scale) behavior to which it is fundamentally related, in this case atomic K.E. and speed.

2) Mass just depends on adding up the number of protons and neutrons. 1 amu for H, 4 amu for He, 16 for O, 12 for C, 14 for N. Except for H they all have a 1:1 ratio of protons and neutrons. (D (deuterium) is an "isotope" of hydrogen which has a neutron, in addition to its proton. It can reasonably be viewed as the most important isotope, partly because it has twice the mass of H...)

Size: For an H atom and an O atom they are nearly the same. Pretty surprising since O has 8 electrons and H has only 1! This mystery is buried in the wave nature of electrons (which we will cover in the last few weeks of this class).

3) This is all about working in Kelvin and scaling. Twice the speed means 4 times the temperature. But only in Kelvin, which is the T scale where v=0 at T=0, and thus the only scale with fundamental physics credibility.

4) See solutions for nice pictures of the modes.


http://people.ucsc.edu/~epaisley/phys1%20-%20quiz2%20sols.pdf