Thread: conduction
View Single Post
  #13   Report Post  
Posted to uk.d-i-y
John Rumm John Rumm is offline
external usenet poster
Posts: 25,191
Default conduction

On 03/06/2021 20:07, williamwright wrote:
On 03/06/2021 14:52, John Rumm wrote:
On 03/06/2021 14:02, williamwright wrote:

If two conductors are merely touched together electricity can flow
between them. That just seems too easy somehow. I mean, just
touching? That's ridiculous. I've always thought that it ought to
need more intimate bonding between conductors for current to flow.

In metals there are usually an abundance of free electrons - these are
very easy to separate from the atom which they orbit, and move to
another one close by. Hence any conductive atom in close proximity can
share its electrons, and allow a current to flow.

Even if the conductors aren't touching, sometimes there's a spark.

Air is an insulator, but it has a breakdown voltage (aka "dielectric
strength") where given enough voltage or "electrical field strength"
you can rip electrons from the atoms, even though they are not usually
"free". The insulator is then said to have become "ionised" and will
become conductive at least while the material remains ionised.

The point at which this happens is an intrinsic property of the
material, but it's also a function of distance distance. For air you
need a voltage difference of around 3kV/mm to cause a breakdown. o to
get a spark to jump a metre you need a megavolt, but only 300V for a
tenth of a mm and so on.

Another question. Why do I wonder about such things?

Because you are a bright spark ?

Thanks John. A good answer.

It was if you gloss over the bit where I left out the "three" in front
of megavolt :-)



/================================================== ===============\
| Internode Ltd - |
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/