Chapter 22 Heat Transfer Review Questions pp 337

Chapter 22 Heat Transfer Review Questions pp. 337 -338 # 1 -20

1. What is the role of “loose” electrons in heat conductors? � The best heat conductors are metals. � Metals have an atomic structure in which the outer electrons are loosely held. � These loose electrons easily transfer energy through the conducting material.

2. Why does a piece of room-temperature metal feel cooler to the touch than paper, wood, or cloth? � The metal is a better conductor. This means the metal allows for heat to be transferred more easily. � Therefore the metal draws the energy (heat) from your hand quickly. � The metal feels cooler to the touch.

3. What is the difference between an insulator and a conductor? �A conductor moves heat quickly while an insulator moves heat slowly.

4. Why are materials such as wood, fur, feathers, and even snow good insulators? � Air is an excellent insulator. � Wood, fur, feathers and snow are all porous materials. They have many air spaces which make them good insulators.

5. What is meant by saying that cold is not a tangible thing? � This is a play on words. When something is tangible you can touch it. � Cold is defined as the absence of heat.

6. How does Archimedes’ principle relate to convection? � Archimedes’ principle states that a warmer fluid is force upward by a denser surrounding fluid. � Convection states that heat is transferred by molecules moving from one location to another. � Archimedes’ principle explains why convection currents occur.

7. Why does the direction of coastal winds change from day to night? � In the daytime the shore heats up more easily than the water (absorbs radiant energy). � Air over the shore rises, cooler air from the water takes its place (sea breeze) � In the evening the shore cools off quicker than water and the process is reversed.

8. How does the temperature of a gas change when it is compressed? When it expands? � When a gas is compressed the temperature increases. � When a gas expands the temperature decreases.

9. Dominoes are placed upright in a row, one next to another. When one is tipped over, it knocks against its neighbor, which does the same in cascade fashion until the whole row collapses. Which of the three types of heat transfer is the most similar? � Conduction � Direct particle to particle contact.

10. What is radiant energy? � Radiant energy is any energy that is transferred in the form of waves. � Radiant energy can move through a vacuum. � Vacuum is the absence of matter.

11. How do the wavelengths of radiant energy vary with the temperature of the radiating source? � Higher temperatures produce energy with shorter wavelengths. � Lower temperatures produce energy with longer wavelengths.

12. Why does a good absorber of radiant energy appear black? �A good absorber appears black because it does not reflect light.

13. Why do eye pupils appear black? � Pupils appear black because the function of a pupil is to absorb the light entering a person’s eye.

14. Is a good absorber of radiation a good emitter or a poor emitter? � ? ? ? ? ? � “Good, otherwise there would be no thermal equilibrium. ” � Remember that heat transfer is about the “Equalizing of temperatures. ”

15. Which will normally cool faster, a black pot of hot tea or a silvered pot of hot tea? �A black pot of hot tea will cool faster. � Black is an excellent absorber of thermal energy. � Which also means that black is an excellent emitter of thermal energy (allows heat to be released easily) � Black allows for the easy transfer of thermal energy in both directions. Absorb and release (emit).

16. Which will undergo the greater rate of cooling, a red-hot poker in a warm oven or a red-hot poker in a cold room (or do both cool at the same rate)? � According to Newton’s law of cooling, the great rate of cooling will occur with the redhot poker in a cold room. � “The greater the difference in temperatures the faster the rate of cooling. ”

17. Does Newton’s law of cooling apply to warming as well as cooling? � Yes.

18. What is terrestrial radiation? � Terrestrial radiation is the radiant energy emitted (released) by the Earth.

19. Solar radiant energy is composed of short waves, yet terrestrial radiation is composed of relatively longer waves. Why? � The Earth’s temperature is lower so it produces waves of longer length.

20 a. What does it mean to say that the greenhouse effect is like a oneway valve? 20 b. Is the greenhouse effect more pronounced for florists’ greenhouses or for the Earth’s surface? � A) It means that only the short wavelengths pass back out. High energy radiation comes in but the greenhouse effect prevents the low energy radiation from escaping. � B) Earth’s surface.