Questions Review Ch 16 1. What are the three common ways in which heat is transferred? Conduction, convection, radiation. Conduction 2. What is the role of "loose" electrons in heat conductors? To conduct energy by collisions throughout a substance. 3. Distinguish between a conductor and an insulator. Electrons are free in conductors, which easily conduct heat. Electrons are bound in insulators, which therefore don't conduct heat well. 4. Touch the metal sides inside of a hot pizza oven with a bare hand and you're in trouble. But hold it briefly in the oven air and you're okay. What does this tell you about the conductivity of metal and air? Metal is a good conductor; air is not. 5. Walk briefly on red hot coals with bare feet and you're probably okay. What is the explanation? Wood is a poor conductor, even when it's red hot. So very little heat conducts from the coal to your feet. 6. Why are materials such as wood, fur, feathers, and even snow good insulators? Because they are composed largely of air spaces, which are good insulators. 7. Does a good insulator prevent heat from getting through it, or slow its passage? No insulator completely prevents heat flow. Instead, an insulator slows the rate of heat penetration. Convection 8. How is heat transferred from one place to another by convection? By actual movement of heated fluid--by currents. 9. How does buoyancy relate to convection? Heated fluid expands, becomes less dense, and is buoyed upward like any fluid less dense than its surroundings.
10. What happens to the volume of air as it rises? What happens to its temperature? Rising air expands when it rises, and cools. 11. When an air molecule is hit by an approaching fastmoving molecule, does its rebound speed increase or decrease? How about when it hits a receding molecule? Increases being hit by an approaching molecule; decreases when hitting a receding molecule. 12. How are the speeds of molecules of air affected when the air is compressed by the action of a tire pump? Molecular speeds increase. 13. How are the speeds of molecules of air affected when the air expands rapidly? Molecular speeds decrease. 14. Why is Millie's hand not burned when she holds it above the escape valve of the pressure cooker (Figure 16.7)? It is in a region of rapidly expanding water vapor, which quickly becomes relatively cool. Cooling is enhanced by a mixture of drawn-in air. 15. Why does the direction of coastal winds change from day to night? During the day, the shore is warmed more than water, so winds blow from water toward the shore. At night, the reverse occurs: the shore cools more than water, and winds blow in the opposite direction. Radiation 16. What exactly is radiant energy? Energy of electromagnetic waves. 17. Relatively speaking, do highfrequency waves have long wavelengths, or short wavelengths? Short wavelengths (see Figure 16.10). Emission of Radiant Energy 18. How does the frequency of radiant energy relate to the absolute temperature of the radiating source?
Frequency and absolute temperature are directly proportional. 19. What is terrestrial radiation? Radiation emitted by Planet Earth. 20. How does solar radiation differ from terrestrial The radiation? sun emits far more energy, and at a higher frequency. 21. What is heat radiation? Electromagnetic radiation in the infra-red part of the spectrum. Absorption of Radiant Energy 22. Since all objects emit energy to their surroundings, why don't the temperatures of all objects continuously decrease? All objects are also absorbing energy from their surroundings. Temperature will decrease only if the object is a net emitter--if it emits more than it absorbs. 23. What determines whether an object at a given time is a net absorber or net emitter? Whether it is colder or warmer than the surroundings. If colder, it is a net absorber. If warmer, it is a net emitter. 24. Which will normally warm faster, a black pot of cold water or a silvered pot of cold water? Explain. A black pot absorbs better than the silvered pot, so therefore it warms faster. Reflection of Radiant Energy 25. Can an object be both a good absorber and a good reflector at the same time? No. Absorption and reflection are opposite processes. 26. Why does the pupil of the eye appear black? Because multiple reflections inside the eye absorb energy, which therefore is not reflected back through the pupil. Cooling at Night by Radiant Energy
27. What happens to the temperature of something that radiates energy without absorbing the same amount in return? It cools. 28. An object radiating energy at night is in contact with the relatively warm earth. How does its conductivity affect whether or not it becomes appreciably colder than the air? If it's a good conductor, energy radiated away is returned by the warm earth, so it doesn't get very cold. But if it's a poor conductor, less energy from the earth warms it and it can become appreciably colder than the air. Newton's Law of Cooling 29. If you want a roomtemperature can of beverage to cool quickly, should you put it in the freezer compartment or in the main part o...