Spring 2010 Midterm Exam

Spring 2010 Midterm Exam - PHYS 3141 Midterm Exam Spring...

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PHYS 3141 Midterm Exam Spring 2010 Problem 1: The box on the left has adiabatic walls. A partition separates a region filled with gas from a region of vacuum. At a certain moment, the partition disintegrates and the gas expands to fill the entire box. The final state is shown on the right. (a) (5 pts) Is any work done during the free expansion of the gas? If so, identify the system that does the work and the system upon which the work is done. If not, explain why not. (b) (5 pts) Is any heat transferred during the free expansion of the gas? If so, identify the system that expels the heat and the system that absorbs the heat. If not, explain why not. (c) (5 pts) Does the internal energy change during the free expansion of the gas? Explain why or why not. Solution: (a) No work is done. The gas cannot exert a force on a vacuum and the vacuum cannot exert a force on the gas. It is true that the volume of the gas changes, but pdV can be identified with dW only for a reversible process (like the expansion of a gas against a piston that provides an opposing
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Spring 2010 Midterm Exam - PHYS 3141 Midterm Exam Spring...

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