PHYS Name: 221 General Physics I Second Exam Spring 2007 Note: Show your work. Correct answers by themselves are not sufficient. Also, watch the significant digits in each problem. 1. The speed of the protons in the solar wind at the Earths orbit averages about 450 km/s. What is the effective temperature of this solar wind component? [This is true even though there are only about 6 protons/cm3 in the solar wind.]
2. A heat engine operates by absorbing 3.45 X 104 J of heat from a hot reservoir and exhausting 2.25 X 104 J of heat to a cold reservoir during each cycle. How much work is done in each cycle, and what is the efficiency of the engine?
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3. A uniform electric field is parallel to the x-axis. In what direction can a charge be displaced in this field without any external work being done on the charge? [Explain briefly.]
4. (a) What is the equivalent capacitance of the circuit at right? (b) What is the charge on each of the capacitors? (Note: E = 9.0 V, C1 = 2.0 F, C2 = 3.0 F, and C3 = 3.0 F.)
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5. A 1250-W hair dryer is connected to 120-V a receptacle. What is the resistance of the filament of the hair dryer and current flowing through it? [Assume 3 significant digits.]
6. If a 2.45-kg mass of aluminum is heated to 190.o C is dropped into a large freshwater lake at 19.5o C, what is the change in entropy of the lake? Assume no heat was lost to the air or the earth around the lake.
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7. A -3.5-C charge is located at -2.50 cm on the x-axis while a 2.7-C charge is located at 1.85 cm on the y-axis. (a) What is the magnitude and direction of the electric field at the origin due to these two charges? (b) What is the electric potential at the origin?
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