Week 21 (Jan. 12 - 16)
Reading: Heat and the First Law (Chap. 20)
Key Topics: ideal gasses, isobaric and isothermal expansion, heat conduction, convection, and radiation.
Key Topics: ideal gasses, isobaric and isothermal expansion, heat conduction, convection, and radiation.
Week 21 Homework Problems:
- Isobaric (constant pressure) expansion of ideal gas: An ideal gas is enclosed in a cylinder with a movable piston on top. The piston has a mass of 8000 g and an area of 5.0 sq. cm. It is free to slide up and down, keeping the pressure of the gas constant. How much work is done as the temperature of 0.20 mol of gas is raised from 20 to 300 deg. C?
- Isothermal (constant temperature) expansion of ideal gas: Five moles of an ideal gas expand isothermally at 127 deg. C to four times its initial volume. Find the work done by the gas and the thermal energy transferred to the system in Joules.
- Heat transport through fat: Suppose that heat from the inside of the human body must travel through a layer of fat 30 mm thick before reaching the skin. Suppose, further, that there are 1.7 square meters of skin on the surface of a person. On a 34 deg. C day, how much heat is conducted from the inside of the human body to the skin in one hour? You may assume that the thermal conductivity of fat is 0.20 watts per meter-degree C.
- Challenge: a steel guitar string with a diameter of 1.00 mm is stretched between supports 80.0 cm apart. The temperature is 0.0 deg. C. The young's modulus of steel is 20e10 N/m^2 and the coefficient of linear is expansion is 11e-6 per deg. C. Find the mass per unit length of the string (assume the density of steel is 7.86e3 kg/m^3). If the fundamental frequency, f, of oscillation is 200 Hz, what is the tension in the string? If the temperature is raised to 30.0 deg. C, find the tension and the fundamental frequency.
