On Thu, 4 Sep 2008 20:28:52 +0000 (UTC) EskWIRED@[EMAIL PROTECTED]
wrote:
| In sci.physics.electromag, extremesoundandlight@[EMAIL PROTECTED]
> wrote:
|
|> use carbon nano fiber as the wire its thin and can su****t a
|> tremedousely high current and voltage witch is directly pro****tional
|> and inversly pro****tional to resistance.
|
| Ummm....using any wire of any thickness and a given resistance per unit
of
| length, why is it that more voltage will yield more current? Is it a
| matter of velocity of electron flow?
More voltage applied to a FIXED resistance means more current. It also
means
more watts in pro****tion to the square of the voltage.
If you have a 160 ohm resistor (one that can handle a LOT of watts), and
apply
120 volts to it, it will have a current of 0.75 amps, and dissipate 90
watts.
if you raise the voltage to 240 volts, the current will now be 1.5 amps,
and
it will dissipate 360 watts.
More voltage -> more current ... when the resistance is the same.
Note that if you apply this to light bulbs or other devices that heat up a
lot, the resistance actually changes, and the calculations are more
complex.
A very large resistor that stays reasonably cool will not be significantly
affected by this.
The physic behind this is concpetually similar to the physics behind
squeezing
water through a hose, or nozzle, or a spongy filter. Increase the
pressure
and you increase the rate of flow.
At the atomic level, the electrons are encountering difficulties in trying
to move. As they do this, they heat things up in the process.
| Why, for example, does one needs to use thicker wires on the low side of
a
| transformer, while on the high side, one can use thinner wires?
|
| I'm not asking to be told that the resistance of the thick wire is
lower,
| so by applyng Ohm's law, we see that....
|
| Instead, I'm asking what is going on at a particle level. And
| additionally, as a corollary question, I'm asking whether the associated
| magnetic field propogates down the length of the wire at a greater
| velocity at higher voltage.
At the particle level, electrons banging around between atoms and
molecules
are losing some voltage, and this translates as resistance.
Some devices, like diodes, have a fixed voltage drop across junctions,
even
as the voltage changes. So in these cases, the current isn't determined
by
that device. But the device in series with the diode will see a lower
voltage. The physics behind this is not something I have studied, yet.
I also know that an electric arc jumping off a conductor has a fixed
voltage
drop, which varies by the material used as the conductor, the gas used as
the
medium, and other factors like temperature and pressure. A voltage
applied
at less than this arc voltage drop simply cannot produce an arc. But
there
will be such a voltage briefly, even on a low voltage system, due to the
magnetic field established by the current flow. The collapse of that
field
when the conductor breaks contact results in a brief overvoltage that can
cause the arc. Otherwise an arc can only be established when the voltage
exceeds the sum of the gas path breakdown voltage, and the arc contact
voltage
drops.
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