Notes • Exam information: Wednesday, in class. Covers Ch t 15-17. Chapters 15 17 • Review Session: Tonight, 7:30-9:30pm, NSH 127 • Reminder: Problem Set due Friday before you leave campus. Please put in box outside of my office. • Colloquium Tomorrow: “Brian Greene: The State of y , 4pm, p , NSH 118 Stringg Theory”, – Will have Office Hours from 5-6pm. Temperature Scales, Temperature Measurement A resistance thermometer is a device whose electrical resistance (in Ohms, ) changes with temperature. A certain resistance thermometer is found to have a resistance of 90.35 when it is placed in water at the triple-point temperature. What temperature is indicated if it is placed in an environment where its resistance is 96.28 ? (Assume the resistance is absolutely linear with temperature.) How would you calibrate the linearity of your thermometer? Thermal Expansion Thermal Expansion Steel railroad tracks are laid when the temperature is -5°C. A standard section of rail is 12.0 meters long. What gap should be left between the rail sections so that there is no compression when the temperature gets as high as 42°C? www.old-dalby.com/Research.htm A physical pendulum, such as a clock, will expand or contract given the ambient temperature. a)Find ) d thee relative e ve change c ge in period pe od P oof a pphysical ys c pendulum versus change in temperature, in terms of its p , . linear coefficient of thermal expansion, b)A clock pendulum made of invar ( = 0.7×10-6 per °C) C) has a period of 00.500 500 seconds and is accurate at 20°C. If the clock is used in an environment with an average temperature of 30 30°C C, what correction must be made to the time after 30 days? The Ideal Gas A pipe closed at the top and open on the bottom contains air at atmospheric pressure. The pipe is 25 m long. It is lowered vertically into a freshwater lake until the water rises half-way up the pipe, pipe as shown in the figure. figure What is the depth y of the waterwater air interface below the surface? Assume the temperature is the same everywhere y and is constant. y The best vacuum that can be attained in a laboratory is about 10-18 atmospheres. How many molecules per cubic centimeter are there in such a vacuum at 22°C? A small hot air balloon has a volume of 15 m3. The air inside is at an average temperature of 75°C, while the air outside has a temperature of 24°C and an average pressure of 1.0 atm. The balloon is tethered to prevent it from floating away, and the tension in the rope is 10 Newtons. Assume the mass of air is 0.029 kg/mol, and that the fabric of the balloon is massless. What is the average pressure inside the balloon?