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Does electric heating violates the laws of thermodynamics

  1. Oct 29, 2011 #1

    mkj

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    hello,
    we have learned that according to the laws of thermodynamics that the efficiency of any machine should be less than one because of the passive components in it. in an electric heating machine all the input electrical energy is converted to heat. Does this make the electrical heater as an efficiency 1 machine, and does this violates the laws of thermodynamics.
     
  2. jcsd
  3. Oct 29, 2011 #2

    Simon Bridge

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    No and no.

    To go over-unity it would have to make more heat than the electrical energy supplied to it.

    At unity does not violate the laws of thermodynamics: entropy is allowed to stay the same in a closed system.
    (It follows that what you were told is not exactly true.)

    An electric heater is seldom a closed system.
    (Which is, in fact, what you were supposed to get from what you were told.)

    https://www.physicsforums.com/showthread.php?t=500095

    Technically a heater is a super-inefficient heat engine ... typically 90-99% of the heat goes to the exhaust. It so happens that we want this heat to warm us up.
     
    Last edited: Oct 29, 2011
  4. Oct 29, 2011 #3

    russ_watters

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    An electric heater is not a machine. It just happens to be a device where you want waste heat. Think of it this way: if you use the heat to heat a boiler and turn a steam engine, then put a brake on it to dissipate the engine's mechanical energy, you'll have the same 100% efficiency of heat production using a 0% efficient steam engine.
     
  5. Oct 29, 2011 #4
    That's analogous to saying: "all the gasoline used in an engine is converted to heat...and power"....ok, so what......it's an inexact statement and not necessarily a reflection of efficiency.
     
  6. Oct 30, 2011 #5
    Passive components.
    mkj - do not mix up efficiency with gain.
    A gearbox may have a gain in rpm or torque, but due to frictional losses, its efficiency will be less than 1 ( ie power out < power in ). And that is not a thermodynamic efficiency, but a mechanical efficiency.
     
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