Sorry for my english and long post again.

After reading this article, I realized that my understanding seemed to be wrong.

I thought that to create conduction current in some wire first we need a "charging" current - a current that will create voltage by build up charges on surface of the wire. These surface charges then create weak electric field inside the wire that drive conduction current (i.e. conduction current will appear only after "charging" process).

In other words, I considered these "charging" currents (e.g. if voltage is changed) to be completely independent of the conduction current.

But in above mentioned article W. G. V. Rosser describes what will happen with wires connected to generator if voltage of the generator will increase:

...Transient currents again flow in the connecting wire in the direction of extra field ΔE. There is again some current flow towards the surface of connecting wire until more charge builds up on the surface of the wire and "guides" the extra current along the connecting wire...

...However, the changes in electric field field intensity (and the associated changes in potential and conduction current) are generally propagates with a velocity comparable to, but less than the velocity of light.

Besides that, after first glance on transmission line theory it turned out that pulse on it consist of both voltage and current. And it seems that the exact value of current already takes into account current required to charge wires to some voltage:

When increasing the capacitance of a double line, some additional electrons are necessary to keep up at given voltage. Therefore the current I is increased in relation to V, corresponding to a decrease of Z = V/I.

So, now I can't understand how all this related.


It seems that I should not separate a currents and it is not necessary to wait for the completion of the transients to get changes in conduction current.

Instead, some change in voltage (assume it increased) propagate down a wires simultaneously with corresponding change in conduction current. And some part of this conduction current is "spent" on charging the wires to given voltage. Additionally, as these surface charges accumulates during propagation process, they amplify electric field inside the wires to maintain the increased conduction current at this new level.

Is this new description correсt ?

  • \$\begingroup\$ There are errors in your quotes that may be changing the meaning -you should quote what is there accurately... \$\endgroup\$ – Solar Mike Aug 21 '18 at 21:09

Yes, current only moves if there is a change in voltage and flows from a higher voltage to a lower one. There is only one current in this case.

In the case of a capacitor, current flows in and out of the device only when there is a change in voltage on the terminals, otherwise the current through the device is zero.

In most cases there is a voltage source which creates a voltage difference and the current flows back to the source.

With static voltages (sometimes physical processes), you can get current without a 'circuit' and return flow back to the source.


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