# Physics 141, Fall 2016.

## Physics 141, Homework Set # 10. Due: 12/2/16, 12 pm (noon).

1.     (50%) WeBWorK set # 10.

2.     (25%) In 1988 telescopes viewed Pluto as it crossed in front of a distant star.  As the star emerged from behind the planet, light from the star was slightly dimmed as it went through Pluto's atmosphere.  The observations indicated that the atmospheric density at a height of 50 km above the surface of Pluto is about one-third the density at the surface.  The mass of Pluto is known to be about 1.5 x 1022 kg, and its radius is about 1200 km.  Spectroscopic data indicate that the atmosphere is mostly nitrogen (N2).  Estimate the temperature of Pluto's atmosphere.  State what approximations and/or simplifying assumptions you made.

3.     (25%) A nano particle consisting of four iron atoms (object 1) initially has 1 quantum of energy.  It is brought into contact with another nano particle, consisting of two iron atoms (object 2), which has 2 quanta of energy.  The mass of one mole of iron is 56 gram.

a.     Using the Einstein model of a solid, calculate and plot ln(W1) versus q1 (the number of quanta of object 1), ln(W2) versus q1, and ln(Wtotal) versus q1 (put all three plots on the same graph).  Show your work and explain how you obtained the results shown.

b.     Calculate the approximate temperature of the objects when they are in equilibrium.  State clearly what assumptions or approximations you made.

4.     (Optional; 25% extra credit) You can download the gasModel.py program from our web site.  This program simulates the motion of 50 gas molecules in a container.  The simulations start with all molecules having the same speed but random directions.  How long does it take for the system to obtain a speed distribution that mimics the Maxwell-Boltzmann speed distribution?

Modify the program to run various simulations with different masses (for example, use tin and lead atoms) and different temperatures (for example, 100 K, 200 K, 500 K, 1,000 K, and 10,000K) and use graphs to compare the average speed obtained with the program with the average speed expected for the Maxwell-Boltzmann speed distribution.  Do they agree for all masses and temperature?  If they disagree, make sure that the disagreement is not due to numerical problems (e.g. is the step size consistent with the expected range of velocities)?  Send the graphs and a brief description of your conclusions via email to Professor Wolfs (wolfs@pas.rochester.edu).

Last updated on Monday, September 26, 2016 8:41

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