"DAVID WILLIAMS" bravely wrote to "HERMAN TRIVILINO"
(05 Jun 05  22:37:54) 
 --- on the heady topic of "Pnu 732" 
 
 -> ->> Say if I had a vacuum tube free floating in space would it 
 -> ->> exhibit a net acceleration when an electron current flowed 
 -> ->> through it? 
 
 -> ->>  M*i*k*e 
 
 ->  DW> Why should it? 
 
 -> Well, because the conduction electrons are colliding with the atomic nuclei

 -> the conducting material.  The nuclei recoil from the collison resulting in
a 
 -> increase in temperature.  Since the charge carrriers are transferring a
nonz 
 -> net momentum to the conductor, the conductor should recoil with a net
nonzer 
 -> momentum.  Or rather, it might, if the conductinmg material were shapped 
 -> correctly. 
 DW> 
 DW> The electrons are travelling in a closed path - part of which is 
 DW> through the vacuum in the tube, and the rest is through various wires, 
 DW> the power supply, etc.. The net momentum of the electrons is zero, 
 DW> since the momentum of the electrons in part of the path is balanced by 
 DW> that of those on the opposite side of the loop. 
 DW> 
 DW> If electrons lose some momentum by collisions with nuclei, a 
 DW> counterbalancing force must be applied to electrons elsewhere to keep 
 DW> the current going. Basically, this is what happens in the power 
 DW> supply.  Also, of course, electrons that are travelling around curved 
 DW> parts of  the circuit must experience a centripetal force. Overall, the 
 DW> net force  on the electrons is zero, so there is no tendency for the 
 DW> vacuum tube  to accelerate through space. 
 
I think we have to consider the power consumed by the tube. Obviously 
ignoring the filament, we need to consider if the tube dissipates 
energy in an unsymmetrical manner and this we assume mostly at the 
plate electrode. Since we know there is a loss of energy there then, 
it is being emitted on one side mostly and depending on the physical 
shape (not a cylinder) it might result in a net motive force. Perhaps, 
it isn't very great but it's still something. 
 
 M*i*k*e 
 
... Cat Physics #2: A cat will assume the shape of its container.
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