Physics 7A Sample Quiz 3 Summer I 2009 1 7A Sample Quiz 3 1) You might know that one of the things that helps control body temperature is letting water evaporate (from a person’s sweaty forehead, from a dog’s tongue, etc.). In this problem you will use the following simple molecule to help give a microscopic explanation of how evaporation leads to cooling. Suppose 4 atoms are held together by chemical bonds each of which has a potential energy represented by the graph shown to the right. These four atoms are arranged as shown below the graph (3 atoms in a plane and the 4 th above the other three) so that each atom forms a bond with each of its 3 neighbors. You have seen the “Atoms in Motion” simulation so you know that the energy gets transferred back and forth between the atoms as they hit each other. Sometimes one atom has a lot of the thermal energy, sometimes it only has a little, and sometimes they all share the thermal energy approximately equally. For this molecule, use this idea of different sharings of the thermal energy (as necessary) to explain 1)
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