Physics 011

Chapter 14: Heat
Practice Questions

Quiz#14

 1 Which of the following is a unit for Internal Energy? Joule kelvin joule/molecule J/s 2 Which of the following is an English unit for heat? Joule Calorie (C) kcal BTU 3 The unit of emissivity is J. J/s. J/m2. none of these. 4 The unit for heat conduction would be a J. J/s. J/m2. J/s*m2. 5 The unit for radiant heat transfer is J. J/s. J/m2. J/s*m2. 6 A spaceship is drifting in an environment where the acceleration of gravity is essentially zero. As the air on one side of the cabin is heated by an electric heater, what is true about the convection currents caused by this heating? The hot air around the heater rises and the cooler air moves in to take its place. The hot air around the heater drops and the cooler air moves in to take its place. There are no conventional convection currents. 7 In a liquid at a given temperature, the molecules are moving in every direction, some fast, some slowly. Electrical forces of adhesion tend to hold them together. However, occasionally one molecule gains enough energy (as a result of collisions) so that it pulls loose from its neighbors and escapes from the liquid. Which of the following can best be understood in terms of this phenomena? A hot water bottle will do a better job of keeping you warm than will a rock of the same mass heated to the same temperature. When a large steel suspension bridge is built, gaps are left between the girders. If snow begins to fall when you are skiing, you will feel colder than you did before it started to snow. When you step out of a swimming pool and stand in the wind, you will get colder than you would if you stayed out of the wind. Increasing the atmospheric pressure over a liquid will cause the boiling temperature to decrease. 8 Radiant energy is proportional to T. T2. T3. T4. 9 Conduction is proportional to Temperature. Temperature Difference. Thickness. Emissivity. 10 Conduction is inversely proportional to Temperature. Temperature Difference. Thickness. Emissivity. 11 If the thickness of a brick is 8 cm and its conductivity is 0.8J/s*m*Co. What is its thermal resistance? 8.8 10 0.1 0.64 12 If a wooden wall is 8 cm thick and has a conductivity of .08 J/s*m*Co, what is its thermal resistance? 8.08 100 1 .0064 13 If a wall is composed of 8 cm of wood and 8 cm of brick, what would be its total thermal resistance? .1 10 1.1 1.0 14 A piece of hot metal is put into an equal mass of water. The water temperature rises 5 degrees and the metal's temperature drops 10 degrees. What is the specific heat of the metal? 2 kcal/kg*C. 1 kcal/kg*C. .5 kcal/kg*C. Not enough information. 15 The specific heat of glass is 0.2 kcal/kg. If you put 1 kg of glass in contact with an equal mass of water and its temperature drops 5 degrees, by how much will the temperature of the water rise? 1 Co 2 Co 5 Co 10 Co 16 How much heat is needed to boil 1 kg of water to steam? 79.7 kcal 100 kcal 539 kcal 32 kcal 17 How much heat does it take to melt 1 kg of ice into water? 79.7 kcal 100 kcal 539 kcal 32 kcal 18 In the formula U=(3/2)nRT what is n? n is the number of moles. n is the number of atoms. n is the number of atoms in the molecule. n is the number of molecules. 19 In the formula U=(3/2)NkT what is N? N is the number of moles. N is the number of atoms. N is the number of atoms in the molecule. N is the number of molecules. 20 What is the internal energy (to the nearest joule) of 10 moles of Helium at 100 K? 5543 J 8315 J 12473 J None of the above. 21 What is the internal energy (to the nearest joule) of 10 moles of Oxygen at 100 K? 5543 J 8315 J 12473 J None of the above. 22 On a clear day at the equator with the sun directly overhead, how long would it take to warm 10 kg of water 15 Co if the emissivity of the 1.0 m 2 surface is 1? 1.5 s 150 s 200 s 628 s 23 On a very clear dry dark night, little radiation is received from the sky. How much energy, in one hour, will a perfectly black object, with 2 m2 of surface area exposed only to the sky, radiate if its temperature is 50 oC ? 2550 J 7.4x104 2.2x106 4.4x106 J 24 Air is a better insulator than fiberglass, yet we fill the air spaces in our walls with fiberglass insulation. Why do we do this? To seal the walls. To cut down on radiation. For support. To 'still' the air. 25 Can you take a picture of a perfectly black dog? Yes, I have done it. No. I am not sure.