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Chapter 24: Problem 44
Silver and iron wires of the same length and diameter carry the same current. How do the voltages across the two compare?
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Does an electric stove burner draw more current when it's first turned on or when it's fully hot?
A power plant produces \(1000 \mathrm{MW}\) to supply a city \(40 \mathrm{km}\) away. Current flows from the power plant on a single wire with resistance \(50 \mathrm{m} \Omega / \mathrm{km},\) through the city, and returns via the ground, which has negligible resistance. At the power plant the voltage between wire and ground is \(115 \mathrm{kV}\). Find (a) the current in the wire and (b) the fraction of the power lost in transmission.
Passage Problems A brownout occurs when an electric utility can't supply enough power to meet demand. Rather than cut off some customers completely, the utility reduces the voltage across its system. Brownouts are most likely on hot summer days, when heavy air-conditioning loads drive up demand for electricity. In a particular brownout, the utility reduces the voltage by \(10 \%.\) During the brownout, the current in conductors whose resistance is nearly independent of temperature a. decreases by approximately \(10 \%.\) b. decreases by approximately \(20 \%.\) c. decreases by approximately \(5 \%.\) d. You can't tell without knowing the resistance.
An immersion-type heating coil is connected to a \(120-\mathrm{V}\) outlet and immersed in a 250 -mL cup of water initially at \(10^{\circ} \mathrm{C}\) The water comes to a boil in 85 s. Assuming no heat loss, and neglecting the heater's mass, find (a) the power and (b) the heater's resistance.
In Fig. \(24.17,\) a \(100-\mathrm{mA}\) current flows through a copper wire \(0.10 \mathrm{mm}\) in diameter, a salt solution in a 1.0 -cm-diameter glass tube, and a vacuum tube where the current is carried by an electron beam \(1.0 \mathrm{mm}\) in diameter. The density of conduction electrons in copper is \(1.1 \times 10^{29} \mathrm{m}^{-3} .\) The current in the solution is carried equally by positive and negative ions with charges \(\pm 2 e\); the density of each ion species is \(6.1 \times 10^{23} \mathrm{m}^{-3} .\) The electron density in the beam is \(2.2 \times 10^{16} \mathrm{m}^{-3} .\) Find the drift speed in each region.
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