1) A coffee-maker contains a heating element that has a resistance of 11 Ω. This heating element is energized by a 120-V outlet. What is the current in the heating element?
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2) A resistor is connected across the terminals of a 9.0-V battery, which delivers 2.3 x 105 J of energy to the resistor in 7.0 hours. What is the resistance of the resistor?
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3) The heating element in an iron has a resistance 20Ω. The iron is plugged into a 120-V outlet. What is the power dissipated by the iron?
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4) There are approximately 102 million TVs in the United States. Each uses, on average, 74 W of power and is turned on for 5.3 hours a day. If electrical energy costs 0.095 dollars per kWh, how much money is spent every day in keeping the TVs turned on?
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5) An electric heater is used to boil small amounts of water and consists of a 14-Ω coil that is immersed directly in the water. It operates from a 120-V socket. How much time is required for the heater to raise the temperature of 0.39 kg of water from 29 °C to the normal boiling point? Take the specific heat capacity of water to be 4186 J/(kg·C°).
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6) The rms current in a copy machine is 7.54 A, and the resistance of the machine is 21.7Ω. What are (a) the average power and (b) the peak power delivered to the machine?
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7) The rms current in a 48-Ω resistor is 0.38 A. What is the peak value of the voltage across this resistor?
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8) A light bulb is connected to a 120.0-V wall socket. The current in the bulb depends on the time t according to the relation I = (0.793 A) sin [(204 rad/s)t].
(a) What is the frequency of the alternating current?
(b) Determine the resistance of the bulb's filament.
(c) What is the average power delivered to the light bulb?
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