Electric Circuits – Understanding EMF in an LC Circuit

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What is the emf of the inductor in an LC circuit that is oscillating at a fixed amplitude, without damping, and without an external energy source? Am I right that the emf is zero when the work done by the inductor is negative?

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EDIT 1: This is a new diagram. I have changed the sign of the emf, as suggested by Alfred Centauri, and I shifted the energy of the capacitor over 90 degrees. My primary question remains the same: is the emf zero when the work done by the inductor is negative.

EDIT 2: My confusion partly came from a statement in the wikipedia article on electromotive force: "devices provide an emf by converting other forms of energy into electrical energy". In a resistor, which does not provide an emf, the energy conversion is the opposite direction: electrical energy is converted to heat. That made me speculate that the inductor provides no emf when it reduces the electrical energy of the capacitor.
The answer by Alfred Centauri clarified the meaning of emf to me, as well as the article "Does the electromotive force (always) represent work?" (link)

Best Answer

Am I right that it is equal to the voltage of the inductor when the inductor is doing positive work, so when the capacitor is gaining energy, and zero for the rest of the time?

No, for an ideal inductor, the inductor emf $\mathscr{E}_L$ is, at all times, equal in magnitude and opposite in sign to the voltage $v_L$ across the inductor.

$$v_L = L \frac{di_L}{dt} = -\mathscr{E}_L$$

But I am curious about the line of reasoning that led you to believe the inductor emf behaves as you describe. Would you edit your question to include it? It might be valuable to others.

Also, I've answered, in more detail, a few related questions here. I'll look them up and post links later.

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