Chapter 20: Q75PE (page 736)
Military aircraft use\({\rm{400}}\;{\rm{Hz}}\)AC power because it is possible to design lighter-weight equipment at this higher frequency. What is the time for one complete cycle of this power?
The time period of the AC power of the military aircraft is \({\rm{T = 2}}{\rm{.50\;ms}}\).
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If two different wires having identical cross-sectional areas carry the same current, will the drift velocity be higher or lower in the better conductor? Explain in terms of the equation , by considering how the density of charge carriers relates to whether or not a material is a good conductor.
Car batteries are rated in ampere-hours ( A - h ). To what physical quantity do ampere-hours correspond (voltage, charge, ...), and what relationship do ampere-hours have to energy content?
Some surgery is performed with high-voltage electricity passing from a metal scalpel through the tissue being cut. Considering the nature of electric fields at the surface of conductors, why would you expect most of the current to flow from the sharp edge of the scalpel? Do you think high- or low-frequency AC is used?
(a) To what temperature must you raise a resistor made of constantan to double its resistance, assuming a constant temperature coefficient of resistivity? (b) To cut it in half?
(c) What is unreasonable about these results?
(d) Which assumptions are unreasonable, or which premises are inconsistent?
(a) Find the voltage drop in an extension cord having a \({\bf{0}}{\bf{.0600}}\;{\bf{\Omega }}\) resistance and through which \({\bf{5}}{\bf{.00}}\;{\bf{A}}\) is flowing. (b) A cheaper cord utilizes thinner wire and has a resistance of \({\bf{0}}{\bf{.300}}\;{\bf{\Omega }}\). What is the voltage drop in it when \({\bf{5}}{\bf{.00}}\;{\bf{A}}\) flows? (c) Why is the voltage to whatever appliance is being used reduced by this amount? What is the effect on the appliance?
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