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100% efficiency?

  1. Feb 15, 2007 #1
    (ok i not sure where this topic goes so ill take a guess its here)

    ok, I hear that nothing is 100% efficienct. some energy is always lost as heat and sound. however, what about heating elements? or electrical heats or whatever, surely the lost heat (and i dont think any sound cause its electrical) isn't really lost because it can be thought of as part of the output?

    can anyone explain to me where I am flawed. thnx
  2. jcsd
  3. Feb 15, 2007 #2

    Andrew Mason

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    Efficiency is measured by Work out/Energy in . Heat is not work. Work + heat always amounts to 100% of the energy.

  4. Feb 15, 2007 #3
    o rite, well my text book (only 16yearold level lol) says efficiency was useful energy out/energy in

    am i right in saying they have used a simpler version for my level then?
  5. Feb 15, 2007 #4


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    Think of (useful)Energy out/Energy in as a ratio that describes the efficiency. Where the highest quotient you can get is 1. You can convert it to a percentage, just multiply it by 100. So if all energy in went to its intended purpose (all energy in was useful work), we have 1*100 = 100% efficiency.
  6. Feb 15, 2007 #5


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    I'm fine with seeing a heating element as 100% efficient, but if it makes you feel better, you lose some in the wires too...
  7. Feb 16, 2007 #6
    lol, thnx for that :D
  8. Feb 26, 2007 #7
    Or you could look at a heating element as being (almost) 100% inefficient. Your lightbulb does useful work in lighting your room, and incidental work in heating it. The incidental work is called inefficiency in the same way that an unwanted plant is called a weed.

    Now, here's the joke. Well meaning people will run out in the middle of winter to replace all their filament bulbs with more "efficient" mini-flourescents, and their baseboard heaters replace the energy they "saved".

    The same point could be made about the winter energy costs of your refrigerator, computer, etc. A watt is a watt is a watt.

    Efficiency refers to a value that we put on things. All of the energy is used; what percentage is used for something we want?

    The reason I suggest that a heating element is 100% inefficient, is that it converts the energy directly to its lowest state. In principle, we could heat our houses with the "waste" heat from other processes.
  9. Feb 26, 2007 #8
    A heating element will output light (EM radiation in general) in frequencies that won't be absorbed by the material in the room to increase its temprature - you can see it as energy loss.
  10. Feb 26, 2007 #9
    I agree - I would say in general converting energy to a state of more disorder is "inefficient".
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