Additionally, this unit is often seen elsewhere when the energy usage of power consuming devices, structures, or jurisdictions is under consideration. This is the scale of American home energy usage, which is on the order of hundreds of kilowatt-hours per month. The electrical energy E used can be reduced either by reducing the time of use or by reducing the power consumption of that appliance or fixture.
This will not only reduce the cost, but it will also result in a reduced impact on the environment. Improvements to lighting are some of the fastest ways to reduce the electrical energy used in a home or business.
Fluorescent lights are about four times more efficient than incandescent lights—this is true for both the long tubes and the compact fluorescent lights CFL. Thus, a W incandescent bulb can be replaced by a W CFL, which has the same brightness and color.
CFLs have a bent tube inside a globe or a spiral-shaped tube, all connected to a standard screw-in base that fits standard incandescent light sockets. Original problems with color, flicker, shape, and high initial investment for CFLs have been addressed in recent years. The heat transfer from these CFLs is less, and they last up to 10 times longer. Privacy Policy. Skip to main content. Yet, Ben is the most "power-full" since he does the same work in less time.
Power and time are inversely proportional. During a physics lab, Jack and Jill ran up a hill. Jack is twice as massive as Jill; yet Jill ascends the same distance in half the time. Who did the most work? Jack does more work than Jill. Jack must apply twice the force to lift his twice-as-massive body up the same flight of stairs. Yet, Jill is just as "power-full" as Jack. Jill does one-half the work yet does it one-half the time. The reduction in work done is compensated for by the reduction in time.
A tired squirrel mass of approximately 1 kg does push-ups by applying a force to elevate its center-of-mass by 5 cm in order to do a mere 0. If the tired squirrel does all this work in 2 seconds, then determine its power. The tired squirrel does 0. The power rating of this squirrel is found by. When doing a chin-up , a physics student lifts her What is the power delivered by the student's biceps?
The work done to lift her body is. Your household's monthly electric bill is often expressed in kilowatt-hours. One kilowatt-hour is the amount of energy delivered by the flow of l kilowatt of electricity for one hour. Use conversion factors to show how many joules of energy you get when you buy 1 kilowatt-hour of electricity. First, convert 1 kW-hr to Watt-hours. Then convert Watt-hours to 3. Since a Watt-second is equivalent to a Joule, you have found your answer.
An escalator is used to move 20 passengers every minute from the first floor of a department store to the second. The second floor is located 5. The average passenger's mass is Determine the power requirement of the escalator in order to move this number of passengers in this amount of time.
Armed with the knowledge that energy consumed is the product of power and time, you can estimate costs for yourself and make the necessary value judgments about where to save energy. Either power or time must be reduced. It is most cost-effective to limit the use of high-power devices that normally operate for long periods of time, such as water heaters and air conditioners.
This would not include relatively high power devices like toasters, because they are on only a few minutes per day. It would also not include electric clocks, in spite of their hour-per-day usage, because they are very low power devices. It is sometimes possible to use devices that have greater efficiencies—that is, devices that consume less power to accomplish the same task. One example is the compact fluorescent light bulb, which produces over four times more light per watt of power consumed than its incandescent cousin.
Modern civilization depends on energy, but current levels of energy consumption and production are not sustainable. The likelihood of a link between global warming and fossil fuel use with its concomitant production of carbon dioxide , has made reduction in energy use as well as a shift to non-fossil fuels of the utmost importance.
Even though energy in an isolated system is a conserved quantity, the final result of most energy transformations is waste heat transfer to the environment, which is no longer useful for doing work.
Skip to main content. Work, Energy, and Energy Resources. Search for:. Power Learning Objectives By the end of this section, you will be able to: Calculate power by calculating changes in energy over time. Examine power consumption and calculations of the cost of energy consumed.
Power Power is the rate at which work is done. Example 1. Calculating the Power to Climb Stairs What is the power output for a Example 2. Calculating Energy Costs What is the cost of running a 0. Discussion The cost of using the computer in this example is neither exorbitant nor negligible. Conceptual Questions Most electrical appliances are rated in watts. Does this rating depend on how long the appliance is on? When off, it is a zero-watt device.
Explain in terms of the definition of power. Explain, in terms of the definition of power, why energy consumption is sometimes listed in kilowatt-hours rather than joules.
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