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Author Topic: What is the flow of current?  (Read 3269 times)

SIMRAN

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What is the flow of current?
« on: 14/12/2010 21:30:03 »
SIMRAN asked the Naked Scientists:
   
What is the direction of flow of conventional and electronic current?

What do you think?
« Last Edit: 14/12/2010 21:30:03 by _system »


 

Offline Geezer

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What is the flow of current?
« Reply #1 on: 14/12/2010 22:09:05 »
Conventional current flows in a circuit from positive to negative, but, because electrons have a negative charge, they actually flow from negative to positive.

Mind you, the electron's polarity might ultimately be a matter of convention too. Perhaps someone can fill us in on that point.
 

Offline JP

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What is the flow of current?
« Reply #2 on: 15/12/2010 04:12:49 »
I think you're right, Geezer.  It's all about conventions.  Electrons are negatively charged because of convention, and conventional currents are a "flow" of positive charges also because of convention.  Mathematically, the flow of positive charges one way is pretty much equivalent (at least in terms of designing basic circuits) to the flow of negative charges the other way.  At the end of the day, the real purpose of current is to send energy from one place to another by pushing around charged particles.

Technically, electrical current can be carried by the flow of any types of charged particles, but electrons tend to be the most common since they can move quite easily in a lot of materials, especially metals.

Did I thoroughly confuse the subject enough?    ;D
 

Offline Geezer

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What is the flow of current?
« Reply #3 on: 15/12/2010 05:15:32 »
I think you're right, Geezer.  It's all about conventions.  Electrons are negatively charged because of convention, and conventional currents are a "flow" of positive charges also because of convention.  Mathematically, the flow of positive charges one way is pretty much equivalent (at least in terms of designing basic circuits) to the flow of negative charges the other way.  At the end of the day, the real purpose of current is to send energy from one place to another by pushing around charged particles.

Technically, electrical current can be carried by the flow of any types of charged particles, but electrons tend to be the most common since they can move quite easily in a lot of materials, especially metals.

Did I thoroughly confuse the subject enough?    ;D

I don't think so. Positive and negative are convenient terms that we use to explain things, but we should not lose sight of that.
 

Offline graham.d

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What is the flow of current?
« Reply #4 on: 16/12/2010 11:10:32 »
What is true, though, is that it is electrons that are the mobile carrier in normal conductors. As you say, the convention is that electrons have a negative charge and the convention is that current flows from positive to negative. So just to be clear to Simran, when we talk of current flow in a wire, the actual movement of charged particles (i.e. electrons) is actually in the opposite direction. If the conventions had have been derived with the knowledge we have today I would doubt that the conventions would be the same.
 

Offline peppercorn

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What is the flow of current?
« Reply #5 on: 16/12/2010 11:16:56 »
I guess I shouldn't mention 'holes' then? >:(... ;)
 

Offline acsinuk

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What is the flow of current?
« Reply #6 on: 16/12/2010 17:07:02 »
DC current in electrolyte or gas may by convention be considered as an electron particle movement but AC current will move at the speed of light and is a 3D electromagnetic energy movement which pepper is correct I think in saying  flows through the spare holes in the outer electron shell of a conductor
CliveS
 

Offline Bill S

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What is the flow of current?
« Reply #7 on: 16/12/2010 17:12:27 »
Quote from: peppercorn
I guess I shouldn't mention 'holes' then?

Go on, mention holes!  In the current thread nothing could be so positively shocking that it would attract a negative response.  ::)
 

Offline Geezer

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What is the flow of current?
« Reply #8 on: 16/12/2010 17:21:44 »
but AC current will move at the speed of light

Surely the alternating current will still propagate at a speed that is a function of the geometry of the conductor relative to the return path and the nature of the dielectric surrounding the conductor.
 

Offline graham.d

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What is the flow of current?
« Reply #9 on: 16/12/2010 21:04:48 »
I guess I shouldn't mention 'holes' then? >:(... ;)

Well yes. perhaps. But I did say conduction in a normal conductor. This is usually metallic where the main particle of conduction are electrons. If you want to look at semiconductors, and in particular p-type semiconductors where the holes dominate the flow, this is a different issue. This discussion could go into the issue of electron and hole mobility and what this means, but this maybe more than intended. In a metallic conductor the electrons are essentially free to move and are the prime charge carriers.

Really I was trying to answer the question in the spirit in which I believe it was intended.
 

Offline acsinuk

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What is the flow of current?
« Reply #10 on: 20/12/2010 10:29:19 »
Hi Graham
The point I am trying to make is that electron particles have mass and cannot move at the speed of light.  Only electromagnetics can move at the speed of light in a telephone cable; say under the ocean and are therefore not particles but volumes of  3D flux.  Our teaching may need to be revised!
CliveS
 

Offline peppercorn

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What is the flow of current?
« Reply #11 on: 20/12/2010 14:41:36 »
But I did say conduction in a normal conductor. ... In a metallic conductor the electrons are essentially free to move and are the prime charge carriers.

Really I was trying to answer the question in the spirit in which I believe it was intended.
Yeah, yeah! You've an answer for everything! ;)
I imagine the OP is wondering what's going on now >:(

The point I am trying to make is that electron particles have mass and cannot move at the speed of light.  Only electromagnetics can move at the speed of light in a telephone cable; say under the ocean and are therefore not particles but volumes of  3D flux.  Our teaching may need to be revised!
Can you explain what you mean by 'electromagnetics'?  I don't think the EM field in (or more correctly around) the conductor propagates at 'c' in practice, does it?

Or do you mean optic fibres when you refer to undersea telecomms 'cables'. Photons () in this will move at 'c' (locally) although the overall transmission speed is somewhat lower along the fibres length.
 

Offline graham.d

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What is the flow of current?
« Reply #12 on: 20/12/2010 17:32:09 »
Hi Graham
The point I am trying to make is that electron particles have mass and cannot move at the speed of light.  Only electromagnetics can move at the speed of light in a telephone cable; say under the ocean and are therefore not particles but volumes of  3D flux.  Our teaching may need to be revised!
CliveS

Electrons don't need to move at the speed of light. When you turn on a tap with a hose on it, the water will flow out almost immediately but the individual water molecules do not flow so as to travel down the hose from one end to the other in that short time. It is just the pressure wave that does so. The flow of electricity is not too dissimilar and need not involve high level physics to understand it in this way. In a wire the individual electrons actually move rather slowly but there is a lot of them.
 

Offline Geezer

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What is the flow of current?
« Reply #13 on: 20/12/2010 18:36:22 »
Signals typically propagate in cables at around one third the speed of light. I seem to remember that popagation times through optical fibres are even slower, for the reason Graham points out.
 

Offline JP

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What is the flow of current?
« Reply #14 on: 21/12/2010 07:29:52 »
Signals typically propagate in cables at around one third the speed of light. I seem to remember that popagation times through optical fibres are even slower, for the reason Graham points out.

In the optical case, the rays are put in at an angle so that they bounce off the walls of the cable as they move.  This means that they arrive somewhat slower than the speed of light, because they've spent some of their time bouncing back and forth rather than moving forward along the cable.
 

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What is the flow of current?
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