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Chapter 4: Q14DQ (page 873)
The battery in the circuit shown in Fig. Q26.14 has no internal resistance. After you close the switch S, will the brightness of bulbincrease, decrease, or stay the same?
The brightness of will increase.
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BIO The average bulk resistivity of the human body (apart from surface resistance of the skin) is about . The conducting path between the hands can be represented approximately as a cylinder 1.6 m long and 0.10 m in diameter. The skin resistance can be made negligible bysoaking the hands in salt water. (a) What is the resistance between the hands if the skin resistance is negligible? (b) What potential difference between thehands is needed for a lethal shock current of 100 mA ? (Note that your result shows that small potential differences produce dangerous currents when the skin is damp.) (c) With the current in part (b),what power is dissipated in the body?
Copper has free electrons per cubic meter. A 71.0-cm
length of 12-gauge copper wire that is 2.05 mm in diameter carries 4.85 A of
current. (a) How much time does it take for an electron to travel the length
of the wire? (b) Repeat part (a) for 6-gauge copper wire (diameter 4.12 mm)
of the same length that carries the same current. (c) Generally speaking,
how does changing the diameter of a wire that carries a given amount of
current affect the drift velocity of the electrons in the wire?
The heating element of an electric dryer is rated at 4.1 kW when connected to a 240-V line. (a) What is the current in the heating element? Is 12-gauge wire large enough to supply this current? (b) What is the resistance of the dryer’s heating element at its operating temperature? (c) At 11 cents per kWh, how much does it cost per hour to operate the dryer?
An idealized voltmeter is connected across the terminals of abattery, and arole="math" localid="1655719696009" appliance is also connected across its terminals. If the voltmeter reads (a) how much power is being dissipated by the appliance, and (b) what is the internal resistance of the battery?
The capacity of a storage battery, such as those used in automobile electrical systems, is rated in ampere-hours .A battery can supply a current offor or for and so on. (a) What total energy can be supplied by a battery if its internal resistance is negligible? (b) What volume (in litres) of gasoline has a total heat of combustion equal to the energy obtained in part (a)? (See Section 17.6; the density of gasoline is .) (c) If a generator with an average electrical power output ofrole="math" localid="1655719210000" is connected to the battery, how much time will be required for it to charge the battery fully?
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