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paul_harris77

- 52

- 0

I am struggling with 2 different problems with the basic concept of inductance and capacitance.

**1)**Firstly, I am not sure if I am understanding correctly how (hypothetically) an initially "charged" inductor can sustain, when short circuited, a constant current.

I am right in saying that, when the inductor is initially "charged" and then short circuited, and the initial current source is removed, the rate of change of current is negative (current decreasing w.r.t the initial current source), and so the inductor reacts by inducing an emf and hence a current proportional to this negative rate of change of current but in the OPPOSITE direction to the original current source?

If this is correct so far, I am at a loss as to what happens next? Surely the induced current starts decreasing since it is depleting the inductor's finite store of energy? Then what would cause an increase in current to keep the current constant, as I can't see when the inductor is being "charged" again to become a current source once again? My reasoning would seem to imply an oscillating AC current being produced, but I think it should be DC?!

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**2)**My other question is as follows:

Starting with circuit with an inductor and a capacitor connected together both "uncharged", if a battery is connected briefly in parallel with them, the capacitor should rapidly charge and the inductor should resist the sudden change in current by dropping a voltage and as a result be barely "charged". Then if the battery is removed, apparently, assuming no resistance, the circuit should indefinitely oscillate at its resonant frequency. I am stuck as to a qualitive explanation of what happens. One site says that the current increases through the circuit as the capacitor voltage decreases, but I thought the current decayed exponentially from a discharging capacitor?!

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Many thanks in advance

Paul