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In alt.engineering.electrical VWWall wrote:
| wrote:
| In alt.engineering.electrical VWWall wrote:
|
| | Actually, a real current will flow until the line's capacitance is
| | charged to the source voltage. When the source is removed, the energy
| | involved will remain until it is leaked off through the inter-wire
| | resistance. If the source is AC, no net energy will "flow", except that
| | lost in the inter-wire resistance. If the line length is long enough at
| | the frequency involved, reflections from the end of an incorrectly
| | terminated transmission line will return to dissipate energy in the
| | source resistance.
|
| That reflection even happens with DC. When the switch closes, you have a
| rising wavefront leading the chargeup of the line. Unless the far end has
| a perfectly matched load, that wavefront will reflect back. This is in
| fact how a lot of very early radio transmissions were tuned, with the
| "switch" being a noisy spark gap, and the "line" being a long wire antenna
| cut to a specific length. You don't even need to have 2 conductors.
|
| That's because a switch closure is not really DC. Resolve a step
| function into a Fourier series, and it has an infinite number of AC
| components. In the case of a single wire, you do need to consider EM
| theory.

Electromagnetic, yes. Electromotive (as someone else suggested), not really.

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