What is the maximum power consumption of a 12.0V portable cassette player that d

Question

What is the maximum power consumption of a 12.0V portable cassette player that draws a maximum of 256mA of current? Answer: At $0.106 per kW*hr, what does it cost to leave a 25.0W porch light on day and night for a year? Do not enter units. Answer: A power station delivers 457kW of power to a factory through wires of total resistance of 3.10Ohm. How much less power is wasted if the electricity is delivered at 51000V rather than 10900V? Answer: Calculate the peak current in a 1.93kilo-Ohm resistor connected to a 120V rms ac source. Answer: A heater coil connected to a 240V ac line has a resistance of 48.7Ohm. What is the average power used? Answer:

Explanation / Answer

10.) Pmax = V*Imax = 12*0.256 = 3.072 Watts 11.) Wattage of light = 25 W Total on time = 365*24 hours = 8760 hours Total energy = 25*8760 = 219000 Watt-hour = 219 kW*hr Cost = 0.106*219 = 23.214 $ 12.) Power wasted if delivered at 10900 volts: Current in wires = 457000/10900 = 41.9 A Power wasted = I^2*R = 5442.391 W Power wasted if delivered at 51000 volts: Current in wires = 457000/51000 = 8.96 A Power wasted = I^2*R = 248.872 W Thus, amount of less power wasted = 5442.391 - 248.872 W = 5193.519 W 13.)Maximum voltag of ac source = Vmax = Vrms*sqrt(2) = 120*sqrt(2) = 196.7 V Max current = Vmax/R = 196.7V/1.93 kohm = 101.97 mA 14.)Avg power = Vrms^2/R = 240*240/48.7 = 1182.75 Watts

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