SMES1202 Thermal Physics Semester 2 2007/2008 Tutorial 3
[Note: The problems below are from Sears and Salinger]
- Compute the work done against atmospheric pressure when 10 kg of water is converted to steam occupying 16.7 m3. [S&S:3-1]
- Steam at a constant pressure of 30 atm is admitted to the cylinder of a steam engine. The length of the stroke is 0.5 m and the diameter of the cylinder is 0.4 m. How much work in joules is done by the steam per stroke? [S&S:3-2]
- An ideal gas, and a block of copper, have equal volumes of 0.5 m3 at 300 K and atmospheric pressure. The pressure on both is increased reversibly and isothermally to 5 atm. (a) Explain with the aid of a P-V diagram why the work is not the same in the two processes. (b) In which process is the work done greater? (c) Find the work done on each if the compressibility of the copper is 0.7 x10-6 atm-1. (d) Calculate the change in volume in each case. [S&S:3-6]
4. (a) Show that the work done in an arbitrary process on a gas can be expressed as
.
(b) Find the work of an ideal gas in the arbitrary process. [S&S:3-8]
5. (a) Derive an equation similar to that in Problem 4 for the work d’W when the temperature of a stretched wire changes by dT and the tension changes by . (b) Find the expression for the work when the temperature is changed and the tension is held constant. What is the algebraic sign of W if the temperature increases? (c) Find the expression for the work when the tension is changed isothermally. What is the algebraic sign of W if the tension decreases? [S&S:3-9]
6. (a) Calculate the work done by one kilomole of an ideal gas in reversibly traversing the cycle shown in Fig. 1 ten times. (b) Indicate the direction of traversal around the cycle if the net work is positive. [S&S:3-17]
Fig.1
7. A mixture of hydrogen and oxygen is enclosed in a rigid insulating container and exploded by a spark. The temperature and pressure both increase. Neglect the small amount of energy provided by the spark itself. (a) Has there been a flow of heat into the system? (b) Has any work been done by the system? (c) Has there been any change in internal energy U of the system? [S&S:3-24]
8. When a system is taken from state a to state b, in Fig. 2 along the path a-c-b, 80 J of heat flow into the system, and the system does 30 J of work. (a) How much heat flows into the system along path a-d-b, if the work done is 10 J? (b) The system is returned from state b to state a along the curved path. The work done on the system is 20 J. Does the system absorb or liberate heat and how much? (c) If and , find the heat absorbed in the processes a-d and d-b. [S&S:3-26] Fig.2