IB Physics II Test #4 Thermodynamics Name:________________________________ Part I: Answer all MC questions on the scantron 1. A beaker contains water at a higher temperature than its surroundings. Which of the following correctly describes the entropy change in the water and in the surroundings as the water cools? entropy of the water entropy of the surroundings A. decreases decreases B. decreases increases C. increases decreases D. increases increases 2. The work done by an ideal gas as it expands isothermally from a state of volume V1 to a volume V2 is W. The work done by the gas as it expands adiabatically from the same initial state to a state of volume V2 is A.zero. 3. B.less than W but not zero. D.greater than W. A hot liquid X has specific heat capacity SH. It is mixed with an equal mass of a cold liquid Y of specific heat capacity SC. The best estimate of the ratio of is A. 4. C. W. B. C. D. The graph shows the variation with pressure p of the volume V of a sample of gas. The work done during the change of state from X to Y is A. zero B. p1(V2 – V1) C.p2V2 – p1V1 D. 5. Some liquid wax is placed in cool air so that the wax freezes. What are the changes, if any, in the entropy of the wax and of the cool air as the wax is freezing? freezing wax cool air A. constant increases B. increases decreases C. decreases constant D. decreases increases 6. An operating refrigerator with its door open is placed in a thermally insulated room. The refrigerator operates for a long period of time. Which of the following correctly gives the change in temperature and the entropy of the air in the room? A. B. C. D. Page 1 Temperature increases increases decreases decreases Entropy increases decreases decreases increases 7. The diagram shows the pressure / volume (p/V) diagram for one cycle PQRS of an engine. In which sections of the cycle is work done on the engine? A.SP only 8. B.PQ only C.SP and PQ only D.RS and SP only When a gas in a cylinder is compressed at constant temperature by a piston, the pressure of the gas increases. Consider the following three statements. I. The rate at which the molecules collide with the piston increases. II. The average speed of the molecules increases. III. The molecules collide with each other more often. Which statement(s) correctly explain the increase in pressure? A. I only B. II only C. I and II only D. I and III only 9. The graph to the right shows the variation with volume of the pressure of a system. The work done in compressing the gas from R to P is A. 5.0 × 105 J. B. 4.5 × 105 J. C. 3.0 × 105 J. D. 0. 10. A substance changes from solid to liquid at its normal melting temperature. What change, if any, occurs in the average kinetic energy and the average potential energy of its molecules? Average kinetic energy Average potential energy A. constant constant B. increases constant C. increases decreases D. constant increases 11. The specific latent heat of vaporization of a substance is greater than its specific latent heat of fusion because A. boiling takes place at a higher temperature than melting. B. thermal energy is required to raise the temperature from the melting point to the boiling point. C. the volume of the substance decreases on freezing but increases when boiling. D. the increase in potential energy of the molecules is greater on boiling than on melting. 12. In one cycle of a heat engine, 300 J of thermal energy is absorbed and 200 J of thermal energy is ejected. The efficiency of the engine is A. Page 2 . B. . C. . D. . Use the following diagram for #13 and #14 13. The specific heat capacity of a metal block of mass m is determined by placing a heating coil in its centre, as shown in the diagram above. The block is heated for time t and the maximum temperature change recorded is Δθ. The ammeter and voltmeter readings during the heating are I and V respectively. The specific heat capacity is best calculated using which one of the following expressions? A.c = B. c = C.c = D.c = 14. Which one of the following is not a source of error in the experiment? A. Some thermal energy is retained in the heater. B. The thermometer records the temperature at one point in the block. C. Some thermal energy is lost from the variable resistor in the circuit. D. The block is heated at its centre, rather than throughout its whole volume. 15. An ideal gas expands isothermally, doing 2500 J of external work in the process. The thermal energy absorbed by the gas in this process is A. zero. B. less than 2500 J. C. equal to 2500 J. D. more than 2500 J. 16. A sample of an ideal gas is held in an insulated container and it undergoes an adiabatic change. The graph shows the change in pressure p with change in volume V as the gas changes from X to Y. Which of the following describes correctly the work done and the change in the internal energy of the gas? Work done Internal energy A. on the gas increases B. on the gas decreases C. by the gas decreases D. by the gas increases Page 3 PART TWO DIRECTIONS: Answer all questions in this part in the spaces provided. Show all work and explain answers clearly where appropriate for full credit. 1. This question is about internal energy and heat. a) The internal energy of a piece of copper is increased by heating it. [3] i) Explain what is meant, in this context, by internal energy and heating. Internal energy: Heating: ii) Define specific heat capacity. [1] iii) The piece of copper has mass 0.25 kg. The increase in internal energy of the copper is 1.2 x 103 J and its increase in temperature is 20 K. Estimate the specific heat capacity of copper. [2] 2. This question is about ideal gases. a) State what is meant by an ideal gas. b) State and explain how the internal energy and the absolute (Kelvin) temperature of an ideal gas are related. [1] [2] c) Point A in the p-V diagram below represents the state of an ideal gas. The number of moles of the gas is 0.64. i) Deduce that the temperature of the gas in state A is approximately 300 K. [1] ii) A quantity Q of thermal energy is supplied to the gas at constant pressure. The temperature of the gas increases to 900 K. Calculate the new volume of the gas. [2] iii) Deduce the work done by the gas in this change of state. [2] d) i) State the first law of thermodynamics. [2] ii) The first law of thermodynamics is a statement of what principle? [1] e) One mole of a second ideal gas is also heated at constant pressure. The increase in temperature of this gas is 30.0 K. The energy transferred to the gas is 623 J and the work done is 249 J. i) Determine the change in internal energy of the gas. ii) Determine the thermal capacity of the gas. f) Another mole of the same gas as that in (e) is heated at constant volume starting from the same state as that in (e). Suggest whether the thermal capacity in this case is equal to, greater than, or less than the answer in (e)(ii). [3] [2] [3]