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A flaw in the electrical current model?

  1. Aug 30, 2011 #1
    A flaw in the electrical current model??

    I'm not a Physicist...please don't change the channel, but I am very interested in Physics and have recently hit a brick wall with the electrical current model.

    If it is said that electrons are the carriers of charge and that they receive this charge from a power supply (AC or DC) and also that electrons travel at incredibly slow speeds (even when varying resistivity is taken into consideration) through a circuit....here it comes, "How is it possible that switching ON a circuit results in almost instant transfer of the energy carried from the electrons to the device within the circuit??"

    Let's say there is 2 metres worth of wiring from power supply to the device itself, surely if the electrons receive their charge from the power supply they would have to travel that 2metres distance in order to make the device work...? I may be using the words energy and charge incorrectly here... as charge is measured in Coulombs and energy in Joules but I hope someone out there can understand my confusion and help.

    I am pretty sure it's not possible for electrons to receive energy/charge from a power supply....travel towards the device, then when said device is switched off hold that charge until the power supply is switched on again...

    Like I said, I am quite obviously not a Physicist...what I know is self-taught (probably only to higher GCSE level) but again I hope someone can help me.

  2. jcsd
  3. Aug 30, 2011 #2


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    Re: A flaw in the electrical current model??

    This is incorrect. Electrons do not "receive this charge" from the power supply. The charge is intrinsic to the electrons, whether they are in a potential field or not.

    Electrons have high speeds (order of hundreds of meters/second). However, the drift velocity is slow. They are moving at random as an ideal gas particle. So the individual speeds can be large, but the collective speed of the whole glob is slow.

    The not-so-good analogy of current flow is to think of a hose of water connected to a faucet that is already filled. When you turn on the faucet, the pressure at one end will get transmitted very quickly to the other end, and water will flow out almost instantaneously. The water that comes out is not the water that came in from the other end. It's the same thing with current flow. There are already conduction electrons in the wire. When you apply a voltage, electrons come in at one end, and other electrons go out at the other.

  4. Aug 30, 2011 #3


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    Re: A flaw in the electrical current model??

    While there are many flaws with water analogy, I find it works extremely well early on when you are studying circuits. If you think about voltage as difference in pressures, almost all of the circuit laws make sense.
  5. Sep 2, 2011 #4
    Re: A flaw in the electrical current model??


    Thank you very much for your reply. I now feel incredibly stupid for not recognising the obvious error in my above statement, of course electrons are intrinsically negatively charged... metallic bonding leaves them freely "floating" around the positively charged metal nuclei (due to protons within). School boy error on my behalf.

    So, if the charge is "within" the electrons themselves, when voltage is increased do they then receive more energy and does this energy move them any quicker? e.g. standard bulb in a series circuit with 1V cell lights up moderately...but with a 3V cell lights up brightly. Is it that the electrons flowing through the filament transfer their charge or the energy given to them by the power supply?? If it's their charge, surely they must be moving quicker in order to deliver their given charge...

    Sorry to be a pain, my misconceptions hold no bounds...from current to potential difference.

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