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What is the physical meaning of negative value of "Thevenin" resistance? Sometimes in the calculations, a negative value of Thevenin resistance appears.

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    $\begingroup$ You should include an example of negative Thevenin resistance in your question. $\endgroup$ – NeutronStar Jan 12 '15 at 15:51
  • $\begingroup$ i do not have the problem now but will post it when i get but i think the physical meaning does not depend on the problem but the concept $\endgroup$ – Mohamed Osama Jan 12 '15 at 15:59
  • $\begingroup$ As an example, a tunnel diode has an operating region where its small-signal equivalent circuit is a Thevenin circuit with negative resistance. This operating region is called the "negative resistance region". $\endgroup$ – The Photon Jan 12 '15 at 17:31
  • $\begingroup$ :) ------------- $\endgroup$ – docscience Jan 12 '15 at 17:32
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    $\begingroup$ And the classical example is the glow tube. $\endgroup$ – The Photon Jan 12 '15 at 17:38
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Negative resistance cannot physically occur in the case where the circuit is linear and contains only passive components (resistors, capacitors and inductors). But for active circuits - usually where amplifiers are applied - a virtual negative resistance can be realized.

The physical meaning of negative resistance is that power is absorbed by the circuit with zero phase shift - rather than dissipated.

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    $\begingroup$ Is "absorbed" really the word you want there? I'd say "generated" instead. $\endgroup$ – The Photon Jan 12 '15 at 17:28
  • $\begingroup$ Generated is synonymous with dissipated, both meaning power leaving the circuit. I do mean absorbed. In the sense that power is going into the circuit. $\endgroup$ – docscience Jan 12 '15 at 17:34
  • $\begingroup$ In that case, I find your answer isn't clear when it says "the circuit" does it mean the circuit that we're making a thevenin equivalent for, or does it mean the circuit that's attached to the circuit whe're making an equivalent circuit for? $\endgroup$ – The Photon Jan 12 '15 at 17:35
  • $\begingroup$ @ThePhoton My answer is more general than the Thevinin equivalence. It applies to either Thevin resistance or just resistance. $\endgroup$ – docscience Jan 12 '15 at 17:41
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    $\begingroup$ @MohamedOsama I'm not saying the negative resistance is a simple energy source; it's rather a 'dependent' energy source. Dependent on the current or voltage applied across the element. Since the resistance comes with a negative sign it will tend to reverse the direction of the dynamic response. So if the response in the circuit was initially converging, adding the negative resistance will likely lead to a diverging response. And on the contrary could help stabilize a feedback loop. Negative feedback leads to stable loops. $\endgroup$ – docscience May 17 '15 at 16:17

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