Teaching Physics with the Physics Suite
Edward F. Redish
You were sick the day of the lab on heat and temperature and you asked you lab partner to explain to you what she had done. She opened her folder and pulled out the graph shown at the right. She said, “We used these temperature probes hooked to the computer. We put them in two beakers with liquids in them and mixed them together. We did this with a number of different liquids. One was always 100 cc of water. We started the computer and then poured the liquid from one beaker into the other and put both temperature probes into the beaker with the liquid and stirred them up. We then continued to take data for about a minute.” A. If the second beaker contained water, what must have been the mass of water in the beaker? Explain your reasoning.
A. If the second beaker contained water, what must have been the mass of water in the beaker? Explain your reasoning.
B. Your lab partner say, “Wait. I don’t think this graph is for water. I remember the stuff in the second beaker smelled funny. It could have been carbon tet (CCl4).” If the second beaker did hold carbon tetrachloride, as she suggests, how much liquid must have been in that beaker? (The specific heat of water is 4184 J/kg-C and for CCl4 it is 866 J/kg-C.)
C. She doesn't remember whether the hot beaker contained the water or the CCl4. Does it matter? If so find the answer for the other arrangement than you considered in B. If it does not, explain why not.
D. From your lab partner’s description of what she did and the graph, she must have poured the two liquids together at t ~ 2 s. Stirring them together doesn’t take long – only a second or two. Yet after 15 s, the two probes in the same beaker with the mixed liquids were reading different values. How did one probe know how to find the hot liquid and the other the cold liquid in the mixed fluids?
Page last modified December 28, 2010: HT09