twisted pair wiring

What's the mass of the field? The electrons themselves do not move very fast at all. You could imagine doing this experiment with a just one of the twisted conductors in use. What would you see? Not much, I suspect.

Sylvia.

suspect.

The electrons' net movement is not very fast. What do you mean by 'mass of the field'? I don't remember hearing that phrase. Maybe I was hung over that day, or, more likely, drunk.

j

Sorry that was a joke > ;-)

The reality is, in the discussions of field, the stuff going on around a pair of 60hz wires going from here to there is minimal. Fold back the in and out, wind them in a coil and stick a piece of iron in there you got ya something.

I think you'll find that the velocity of an individual electron is not very great. As for the mass of a field, we need that notion if we want to deduce the existence of a force arising from the accelaration of the electricity as it goes round the twists in the conductor.

In reality a field contains energy, so it necessarily also has mass, they being the same thing. One can calculate the energy per unit length of conductor and thereby the mass. I haven't done the sums, but I'm sure it comes to a very small amount.

Sylvia.

Lightbulbs would unscrew themselves, if the spin was counter-clockwise. And you DON'T want to see what it does to the bread in your toaster! :-)

An electron is moving some 10^6 m/s as it pinballs around from atom to atom. That's no slouch.

I'll have to look around for some field-mass information. I do understand your energy-mass equivalence argument.

j

The calculation is straight forward I think. Suppose we have 1kW going through the cable, and that the electric field propagates at 2/3 the speed of light. Then the energy per meter length is 1000 Joules/s divided by 200,000,000 m/s, which is 0.000005 Joules per metre.

E = mc^2, so m = E / (c^2)

Applying this gives me 5.55 * 10^-23 kilograms/metre.

Like I said - rather small.

Sylvia.

Not too likely to snap any insulator strings, hey? The part I didn't follow was this sentence

"As for the mass of a field, we need that notion if we want to deduce the existence of a force arising from the accelaration of the electricity as it goes round the twists in the conductor."

What force are we wanting to deduce arises from the acceleration of the electricity?

j

We need to go back to Greg's tongue in cheek comment comment:

"Since this type of "army" wire has about 50 twists per meter you could say the electricity was spinning at about 900 million RPM. It's lucky that the stuff coming back is going in the opposite direction and nulling out the field or it would pull all of the nails out of the wall."

So I took this as a claim that were the field not to be "nulled out", then there would be forces large enough to detatch the cable from the wall.

Something travelling at constant speed along a helical path, as with a twisted pair cable, can be considered to have a circular motion superimposed on a linear motion. The linear component is constant, so there is no force involved. The circular component of course involves acceleration towards the centre of the circle. But for this to involve a force, the thing doing the moving has to have mass. Since it was the field that was allegedly going to have this effect, we need to consider the mass of the field.

If the field is moving along the cable (something I'm rather doubtful about), then the real outcome would be that the helix would tend to be stretched outwards, perpendicular to its axis. Over a complete turn of the helix, the forces would cancel out, so there'd be no danger of the cable pulling away from the wall anyway.

As it is, it looks like the effect, even if real, is likely to be too small to be measurable, being completely overwhelmed by electromagnetic effects.

Sylvia.

Ohhhhhhhhh ... I was massively confused. Now I think I get what you're saying. You're talking about a field whipping around the wire and tearing it loose, almost like a hula- hoop or something could whip around a wire and tear it loose due to its mass pulling on the wire. Then you're saying that even if the field were doing so, it wouldn't have a whole lot of mass with which to tear the cable away from the wall, and the forces would balance out over a turn anyways.

When I read his joke, I took him to mean that any nearby nails would be pulled from any nearby walls due to the magnetic fields that would result from electrons traveling along what's essentially a solenoid at a massive

900 million RPM. Then I thought you were saying that for a magnetic field to pull nails out of a wall, the field had to apply a force to the nails ... and that the nails would want to apply a force back on the field (as per Newton) ... and that for nails to apply a force (F=ma) to a field, the field needs mass. So you can see why I didn't seem to be able to follow what you were saying, it's easily explained by the fact that I'm an idiot. j

Here stupid :-) They're smarter over there. :-)

comp.home.automation

Gerald Newton has limited horizons. (Meaning he *can't* provide an intelligent answer.)

Beyond that it doesn't appear that this thread got much play in comp.home.automation at all. B Fuhrmann was the only one who discussed it on technical merits, and he missed at least half of the effects. I would have expected his response in this group, because he left out any consideration of something like X10, which is more topical in c.h.a than here.