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Calc the energy saved and cost of running a fluorescent lamp vs. conventional lamp?
A 21.0 W energy-efficient fluorescent lamp is designed to produce the same illumination as a conventional 25.0 W lamp.
How much energy does this lamp save during 240.0 h of use? Answer in units of J.
If electrical energy costs $0.080/kW(times)h, how much money is saved in 240.0 h? Answer in units of dollars.
A Watt is a Joule per second
240 hours = 864000 seconds
Energy used by fluorescent lamp = 21 * 864000 = 18, 144, 000
Energy used by conventional lamp = 25 * 864000 = 21, 600, 000
Energy saved = 21, 600, 000 - 18, 144, 000 = 3.46 x 10 ^6 J
The cost is given in units of dollars per kilowatt per hour
So you need to multiply by the number of hours and the number of kilowatts difference between the lamps
0.080 * 240 * 0.004 = 0.077 dollars saved
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