Chapter 4: Q17DQ (page 777)
In electronics it is customary to define the potential of ground (thinking of the earth as a large conductor) as zero. Is this consistent with the fact that the earth has a net electric charge that is not zero?
The electric potential of the earth is not zero.
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(a) At room temperature, what is the strength of the electric field in a
12-gauge copper wire (diameter ) that is needed to cause a
current to flow? (b) What field would be needed if the wire were made of silver
instead?
A 1500-W electric heater is plugged into the outlet of a 120-V circuit that has a 20-A circuit breaker. You plug an electric hair dryer into the same outlet. The hair dryer has power settings of 600 W, 900 W, 1200 W, and 1500 W. You start with the hair dryer on the 600-W setting and increase the power setting until the circuit breaker trips. What power setting caused the breaker to trip?
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?
When switch Sin Fig. E25.29 is open, the voltmeter V reads 3.08 V. When the switch is closed, the voltmeter reading drops to 2.97 V, and the ammeter A reads 1.65 A. Find the emf, the internal resistance of the battery, and the circuit resistance R. Assume that the two meters are ideal, so they don’t affect the circuit.
Fig. E25.29.
An electron at pointinFig. E27.15has a speedofFind (a) the magnitude and direction of the magnetic field that will cause the electron to follow the semicircular path fromto, and (b) the time required for the electron to move fromto.
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