Chapter 24 review


    Conceptual questions
      Section 24.2
      1. To cool a miniature circuit, an engineer glues it to one end of a metal rod. She then dips the other end of the rod in water. Which of the following would speed up the rate at which the circuit is cooled? (More than one choice may be correct.)
        1. replacing the first rod with a shorter one
        2. immersing the rod in warmer water than before
        3. replacing the metal rod with a wooden one of the same shape and size
      2. Easy Once again, an engineer glues a small circuit to one end of a metal rod to help keep it from getting too hot. She then dips the other end of the rod in water. Each of the following actions will change one variable in the right-hand side of the conduction formula, P = (κA/LT. Which variable applies to each of the following actions?
        1. replacing the first rod with a shorter one
        2. immersing the rod in warmer water than before
        3. replacing the metal rod with a wooden one of the same shape and size
      3. Easy Heat conducts across a wall according to the equation P= κA L ΔT Which of the following choices best completes the sentence?
        The power conducted decreases as
        1. the height of the wall increases.
        2. the width of the wall increases.
        3. the thickness of the wall increases.
        4. the conductivity of the insulating material increases.
      4. Medium In the heat conduction equation, the energy-transfer rate (P) depends on a material’s thermal conductivity (κ), which has SI units of watts per meter per degree Celsius. By contrast, in the heat convection formula, the heat transfer coefficient has SI units of watts per squared meter per degree Celsius. Explain this difference.
      Section 24.3
      1. Which of the following statements correctly compares radiation with conduction and convection?
        1. Only radiation requires a temperature difference in order to transfer thermal energy from one place or object to another.
        2. Radiation can travel through a perfect vacuum, whereas conduction and convection both require the presence of matter.
        3. In all three cases, the rate of energy transfer (or power P) is proportional to the difference in temperature.
      1. Which of the following astronomical objects will have the peak of its blackbody radiation at the shortest wavelength?
        1. a molecular cloud at a temperature of 10 K
        2. a high-mass star with surface temperature of 10,000 K
        3. diffuse, ionized gas at a temperature of 106 K
      2. Easy Most stars behave more or less like blackbodies, with their surfaces approximately obeying the Stefan–Boltzman law. Use this fact to explain how some relatively cool stars (red giants) can emit much more radiant energy than some relatively hot stars (white dwarfs)—even though the dwarfs have much higher temperatures.
      3. Medium Sea level has been measured for centuries using tide gauges, but more recently it has been measured using satellite data. Research these two sets of data to answer the following questions.
        1. Analyze each approach. How does each measurement technique work? Provide a written explanation of the technical details for each of the two processes.
        2. Critique each method and compare each method to the other. Would you trust one set of measurements more than another? Why?
        3. Does either data set or both show a trend over time in the change of the average sea level? Does the trend appear significant?
        4. Compare each independent data set to the other and evaluate them. Do they agree with each other?
      4. Medium One objection to scientific evidence for global warming is that the temperature measurements are unreliable, possibly because some temperature gauges are situated too close to buildings. Research the topic of temperature measurements and global warming.
        1. Analyze the measurement techniques, particularly the standard method of how temperature gauges should be mounted for weather measurements.
        2. Critique whether or not siting issues create systematic errors in the global warming temperature data.
        3. Evaluate whether the warming trends are compromised by thermometer gauge siting issues.
      5. Challenging While the Antarctic land ice sheet has been shown to be losing mass by melting, a consequence of climate change, the amount of Antarctic sea ice has been increasing. How can this be? (Hint: Think about the freezing point of fresh and salt water.)

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