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power loss/heating question

Discussion in 'General Electronics Discussion' started by komalbarun, Jul 4, 2013.

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  1. komalbarun

    komalbarun

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    Nov 25, 2011
    P= I x I x R

    power is lost as heat.

    What I understand is that,in wires, joules are lost. The loss of of joules cause heating.
    How is it so? and why are the joules lost?
     
  2. BobK

    BobK

    7,682
    1,688
    Jan 5, 2010
    Electrons are moving through the wire. They bump into things, losing electrical energy and creating heat energy by making the things they bump into move

    Bob
     
  3. davenn

    davenn Moderator

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    Sep 5, 2009
    R = resistance
    R is the reason for the loss

    this is why in long power transmission lines they use really high voltages 220kV etc
    as this reduces the current and therefore the power loss

    Dave
     
  4. NuLED

    NuLED

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    Jan 7, 2012
    The energy (measured in joules) can be "lost" (it is not really "lost" because it is behaving naturally) by energy conversion into other forms of energy. Heat that you can feel is one thing. It can also be in the form of radiation that you cannot see, and even radio waves, etc. All of this takes energy. The energy conversions happen because of the way the electrons move around and in some cases we take advantage of this by INCREASING the specific energy we want, such as heat (boiling water) or light (LED, light bulbs, etc.) or radio broadcast (Wi-Fi, etc.).

    So actually you have the same amount of energy, but now it has been converted into all these things (which has radiated away).
     
    Last edited: Jul 5, 2013
  5. davenn

    davenn Moderator

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    Sep 5, 2009
    you missed the point, no you don't, because it has been lost to those other forms and is no longer there to be used by the circuit :)

    the point is, you loose electrical energy = not as much useable power at the far end of the cable/transmission line from the generator
    or even in a smaller local battery powered circuit. keeping resistance as low as possible minimises losses

    hence why EHT is used as I said in my previous post so as to maximise the available useable power at the consumer end

    Dave
     
    Last edited: Jul 5, 2013
  6. komalbarun

    komalbarun

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    Nov 25, 2011
    by "things" you mean filling holes and getting out of orbit again or impurities? I still find it kind of hard to understand how the electrical energy is lost though. I guess I will simply consider it as is, that is, the higher R the more the power loss.
     
  7. NuLED

    NuLED

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    Jan 7, 2012
    I was quite new at this also recently but here is how it is: The energy conversion is quite common really. You can see it all around you as wires heat up, glow, etc. and even our sun emits radio waves.

    In fact to START electrons getting excited so they move around, you INTRODUCE energy into the system, such as heat (thermoelectric), light (photovoltaic), physical (piezoelectric), magnetic disturbance (electromagnetic generation), etc. or induce chemical reactions that liberate electrons. So you give them a kick in the butt, and these electrons get off their butts and run around like mad, and bump into other electrons, annoy the heck out of them, and they start running around. This is current flow. :-D

    The OTHER SIDE of this is when the electrons, which have been agitated out of their orbits (and leaving behind holes) go back into these "holes" and into orbits (as you said). Now, they have DROPPED energy levels. And by going back to a lower state of energy, they RELEASE their previously held energy.

    And this energy is then released in whatever electromagnetic radiation, which is "lost" as you do not recapture it, leading to the power loss over distance and time.

    Theoretically if you recapture, say, the heat lost from the resistors, you can reconvert that energy back into electrical motive energy but practically this is impossible.
     
    Last edited: Jul 7, 2013
  8. BobK

    BobK

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    Jan 5, 2010
    Electrons bound to molecules. The electrons carrying the current are free electrons. The amount of free electrons are what makes something a conductor.

    Bob
     
  9. komalbarun

    komalbarun

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    Nov 25, 2011
    Thanks ;-)
     
  10. Dmark

    Dmark

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    Jul 12, 2013
    A we know power lost in an electrical wire is governed by the equation
    Power = Current squared x resistance
    So to reduce the power loss, we just have to reduce either the current or the resistance. To reduce the resistance of a wire, we need to make it larger. There will be more metal to carry the current, so the resistance will be lower. Unfortunately, we would soon end up with an enormous wire, which would be hideously expensive.
    The better solution is to reduce the current. This has the advantage that if we can reduce the current by ten times, we will reduce the power loss by a hundred times! (Remember, power loss in wires is equal to current squared times resistance.)
    How do we reduce the current and still transmit the same power?
    Simply increase the voltage. Remember, Power = Voltage x Current. If we increase the voltage by 10 times, we reduce the current by 10 times, and this reduces the power lost in the wire by 100 times.
     
  11. komalbarun

    komalbarun

    67
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    Nov 25, 2011
    thnx but i know all that, and nuled already gave me the answer to what i needed to know, anyways i appreciate the help ;)
     
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