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Chapter 20: Q19CQ (page 731)
What are the two major hazards of electricity?
Heat and electrical shock are the two most serious dangers linked with electricity.
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With a \(1200\;W\) toaster, how much electrical energy is needed to make a slice of toast (cooking time \(1\) minute)? At \(9.0{\rm{ }}cents/kW/h\), how much does this cost?
In which of the three semiconducting materials listed in Table 20.1 do impurities supply free charges?
(Hint: Examine the range of resistivity for each and determine whether the pure semiconductor has the higher or lower conductivity.)
(a) Redo Exercise\({\rm{20}}{\rm{.25}}\)taking into account the thermal expansion of the tungsten filament. You may assume a thermal expansion coefficient of\({\text{12}} \times {\text{1}}{{\text{0}}^{{\text{ - 6}}}}{\text{ / C}}\).
(b) By what percentage does your answer differ from that in the example?
What would be the maximum cost of a CFL such that the total cost (investment plus operating) would be the same for both CFL and incandescent \(60\;W\) bulbs? Assume the cost of the incandescent bulb is \(25{\rm{ }}cents\) and that electricity costs \(10{\rm{}}cents/kW/h\). Calculate the cost for \(1000{\rm{ }}hours\), as in the cost effectiveness of CFL example.
You are riding in a train, gazing into the distance through its window. As close objects streak by, you notice that the nearby fluorescent lights make dashed streaks. Explain
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