TB_chapter17 - Chapter 17 Current and Resistance CHAPTER 17...

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Chapter 17, Current and Resistance C HAPTER 17 Conceptual Questions C1. A wire 1 mm in diameter is connected to one end of a wire of the same material 2 mm in diameter of twice the length. A voltage source is connected to the wires and a current is passed through the wires. If it takes time T for the average conduction electron to traverse the 1-mm wire, how long does it take for such an electron to traverse the 2-mm wire? a. T /4 b. T c. 4 T d. 8 T C2. A wire has resistance R . A second wire has twice the length, twice the diameter, and twice the resistivity of the first wire. What is its resistance? a. 8 R b. R c. R /4 d. The resistance is not given. C3. Resistor A has twice the resistance of resistor B. When individually connected across a given potential difference, which one dissipates the most power; and when connected in series across the same potential difference, which one dissipates the most power? C4. If a light bulb has half the resistance of a 100-W lightbulb, what would be its wattage? Assume both bulbs are attached to the same 120-V circuit. C5. When the voltage across a nonohmic resistor is doubled, the current through it triples. What happens to the power delivered to this resistor? 35
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Chapter 17, Current and Resistance 17.1 Electric Current 1. The current in an electron beam in a cathode-ray tube is measured to be 70 μ A. How many electrons hit the screen in 5.0 s? ( e = 1.6 × 10 - 19 C) a. 2.2 × 10 11 electrons b. 8.8 × 10 13 electrons c. 2.2 × 10 15 electrons d. 8.8 × 10 18 electrons 2. A wire carries a steady current of 0.1 A over a period of 20 s. What total charge passes through the wire in this time interval? a. 200 C b. 20 C c. 2 C d. 0.005 C 3. In a certain material there is a current of 16 A flowing through a surface to the right, and there is an equal amount of positive and negative charge passing through the surface producing the current. How much negative charge passes through the surface? 17.2 A Microscopic View: Current and Drift Speed
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