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Author Topic: What happens to electrons inside a disconnected cable?  (Read 2850 times)

ian

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ian asked the Naked Scientists:
   
When I disconnect my computer from the power cable but leave the power cable plugged in to the mains, what happens to the flowing electrons in the cable (i.e. the electricity) - do they stop?

What do you think?
« Last Edit: 30/04/2011 06:01:02 by _system »


 

Offline yor_on

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What happens to electrons inside a disconnected cable?
« Reply #1 on: 30/04/2011 14:59:12 »
Let me guess :)

If we assume it to have a 'live current' then also assume that there is no potential for that current to 'jump' and so find a new path it will build a potential that will express itself as heat. If the wire is dimensioned for that heat it won't matter but if it's not the plastics, rubber, whatever material it is, probably will degrade and so allow the two wires to short circuit, starting a fire.

What you're really wondering is how electricity 'works' right?
Well, so am I :)
==

No I'm wrong there, as long as we're talking about a clean cut and no interference the wire will be no different than the outlet it came from. But I still expect heat.
« Last Edit: 30/04/2011 15:02:00 by yor_on »
 

Offline syhprum

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What happens to electrons inside a disconnected cable?
« Reply #2 on: 30/04/2011 16:13:51 »
Yor_on "But I still expect heat"
surely once the outlet of the cable is disconnected the only current flowing with associated movement of electrons will be due to the capacitance between the conductors.
At power frequencies this current will be tiny also any associated heating effect.
« Last Edit: 30/04/2011 16:17:22 by syhprum »
 

Offline graham.d

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What happens to electrons inside a disconnected cable?
« Reply #3 on: 30/04/2011 16:50:49 »
When power is flowing the electrons, which are jiggling about thermally and (in a conductor) are moving from atom to atom, drift under the influence of the applied electric field. Any individual electron does not move far but, like water flowing in a pipe, some will come in at one end and others will go out the other end. If the voltage applied is AC, the same thing applies except that the electrons will drift one way then the other at the 50 or 60Hz frequency. Because there is a + and - supply the movement will be in opposite directions in each wire. If the circuit is broken the electric field will not be present (at least not much, except that established capacitively between the wires) and the electrons will resume their random, thermal dance. As Syphrum says, there will be a very small current (net coherent movement of the electrons) due to the fact that the circuit is not completely broken and there will remain a small capacitance between the two wires. This will use a tiny amount of power which will dissipate as heat in the wires (this is practically negligible though).
 

Offline yor_on

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What happens to electrons inside a disconnected cable?
« Reply #4 on: 30/04/2011 17:31:17 »
Yep, that's the heat I was thinking of. Induced through the electromagnetic field created by the current.
 

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What happens to electrons inside a disconnected cable?
« Reply #4 on: 30/04/2011 17:31:17 »

 

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