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Using energy in different forms

  1. Sep 26, 2015 #1
    ok energy is supposed to change its nature as its used, say electricity. Yet there is rules in electrical work that call this degradation. I.E. the 3 foot drop rule for figuring out size of wire to allow current flow. Now if this is true and you can't recycle energy how then can we say that it is not finite. My question is if energy does change states how do harness the new states.
     
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  3. Sep 26, 2015 #2

    mfb

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    Do you know the concept of entropy? It can only increase. As an example, electric energy (usually) has a low entropy, so you can use it in many ways that all increase the entropy a bit. Thermal energy has a high entropy, so it is harder to use it.
     
  4. Sep 26, 2015 #3

    Nugatory

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    "3 foot drop rule"? That makes no sense here. Did you mean a rule about voltage drop?
     
  5. Sep 26, 2015 #4
    that is true but when you use enough electrical currant it generates heat, this also taken into account by the thermal induction principles but my question still stands. Even allowing for entropy which in it self follow mechanics based on corresponding variables can be predicted to allow for change in state. I.E. probability mechanics, the rules we use for statistics and such. How do we harness the direct change in states of energy?
     
  6. Sep 26, 2015 #5
    In electrical work when you have figure out what size of wire oversize your wire to allow reduction in power. Now this is done by distance, you x every so many feet so you increase the wire size to compensate for it.
     
  7. Sep 26, 2015 #6

    Nugatory

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    Ah - Thanks, now I understand. For the wiring that I'm most familiar with (North American residential) those corrections don't come into play until you're dealing with lengths very much longer than three feet.
     
  8. Sep 26, 2015 #7

    mfb

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    Right, that direction is easy. Reverting it doesn't work. That is the point of entropy.

    I don't get what you are asking.
    What do you mean with "harness the direct change"?
     
  9. Sep 26, 2015 #8
    Ok so if we know the state change is to heat then how do harness that heat effeciently and what state comes after it? Basicall how do we continually harness the changes in state of energy?
     
  10. Sep 26, 2015 #9
    NP I've done a lot of commercial and industrial work and I been to college for it as well. Still you may not be aware but those calculations are still used in residential when you bring power into a home and to the box.
     
  11. Sep 26, 2015 #10

    mfb

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    If you want to heat something, make sure you have a good thermal connection between heating element and the thing you want to heat.
    The energy itself is interesting, not its transformation - that is just a necessary step to get the right type of energy. You cannot make a cycle out of it, entropy prevents that. You constantly lose, and you need fuel, light, electricity or something else to keep your process running, no matter how the process looks like.
     
  12. Sep 26, 2015 #11
    But doesn't that go agaist eistien's theory say that energy can be niether created not destroyed?
     
  13. Sep 26, 2015 #12

    Drakkith

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    No, because the energy wasn't destroyed. It still exists, it just can't be harnessed for use.
     
  14. Sep 26, 2015 #13
    so then following that logic lets say then that for the point of argument that energy then is not really being lost maybe it is taking on multiple states then while we are focused on the obvious change we lose sight of the more subtle ones?
     
  15. Sep 26, 2015 #14

    Drakkith

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    We use a machine designed to harness that energy for work. For example, a dam uses a water turbine to harness the gravitational potential energy and kinetic energy of the falling water and convert it to electrical energy. We can then use another machine to use that electrical energy and perform work. We could use an electric motor to turn a wheel for example.
     
  16. Sep 26, 2015 #15
    I agree with this concept but I feel that there is a lot of wasted potential in the uses of energy and how it's harnessed. So how about this then how does a rechargeable battery side step entropy?
     
  17. Sep 26, 2015 #16

    Drakkith

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    Energy cannot 'take on a state'. It is not an object or a substance. During any process which converts energy into another form, some of that energy is lost, meaning that it cannot be used to perform useful work. For example, an internal combustion engine loses energy in the form of heat that isn't used to perform work on the piston and ultimately move your car. We can't avoid this loss. There's no way to use 100% of the energy for work.

    I agree that lots of wasted energy could be harnessed, but in most cases it's simply not economical to do so.

    Also, a battery doesn't side step entropy. Why would it?
     
  18. Sep 26, 2015 #17
    supposedly energy is lost over use a Rechargeable battery isn't making new energy and therefore recycling or storing more energy at what point does entropy come into play.

    What can't we use 100% of all possible energy is it a set rule or something that no one has figured out how to do yet?

    And speaking of rechargeable batteries why is the excess energy not stored for future use. Similar to the battery stores of Alaska. Say with the Hydro electric dam you mentioned say we loose I don't know 20% of energy, how much of that could be used if a battery store was set up.
     
  19. Sep 26, 2015 #18

    Drakkith

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    A rechargeable battery simply stores energy as chemical potential energy. Energy is lost in both the charging and discharging processes. For example, my cell phone gets noticeable warm after I use it for a while, partly because the battery is losing energy as heat during discharge.

    As far as we know, it's a set rule.
     
  20. Sep 26, 2015 #19
    sorry to have bothered you it seems that my post will be deleted.
     
  21. Sep 26, 2015 #20

    sophiecentaur

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    The aim of all good Engineering is to make an Energy conversion system as efficient as possible but there are fundamental limits - as when the maximum possible efficiency of a heat engine is totally limited by the temperature range it operates between. This thermodynamic efficiency is always further reduced by practicalities.
    The entropy changes in a rechargeable are not the same as in a heat engine so there is no 'sidestepping'. The charge / discharge cycle still involves loss - if only because of resistance in the circuit.
     
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