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## Main Question or Discussion Point

Does quickly shorting out an inductor in series with a capcitor create a small emp?

- Thread starter Agnostic
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Does quickly shorting out an inductor in series with a capcitor create a small emp?

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SGT

Foe real elements you will have a damped sinusoid.

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berkeman

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What are you shorting out? What are the initial conditions of the inductor and capacitor?Agnostic said:Does quickly shorting out an inductor in series with a capcitor create a small emp?

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Sorry for the lack of clarity.berkeman said:What are you shorting out? What are the initial conditions of the inductor and capacitor?

A highly charged ideal physics capacitor and inductor in series by means of an ideal physics wire.

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berkeman

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You still haven't specified the initial conditions. Do you mean that you have an inductor connected in series with a capacitor, and the capacitor has an initial voltage Vo on it, and the initial inductor current Io is zero? And then you complete the circuit with a switch to "short them out"?Agnostic said:Sorry for the lack of clarity.

A highly charged ideal physics capacitor and inductor in series by means of an ideal physics wire.

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A capacitor connected in series to an inductor. At t=t.x, the capacitor has been discharged as much as possible into the inductor.berkeman said:You still haven't specified the initial conditions. Do you mean that you have an inductor connected in series with a capacitor, and the capacitor has an initial voltage Vo on it, and the initial inductor current Io is zero? And then you complete the circuit with a switch to "short them out"?

Not switching a switch to short it out instantly. But shorting it out rather quicly, saying it takes like x nanoseconds to short it out.

- #7

SGT

Since the voltage in the inductor is [tex]L\frac{di}{dt}[/tex], making [tex]dt = 0[/tex] causes the voltage go to infinity.

A physical inductor has associated to it a winding resistance and a winding capacitance, so in practice you will have a high frequency, high voltage damped oscillation.

If the amplitude of the voltage is high enough, the air in the open gap can be ionized and a spark appears. This is observable when you switch off a fluorescent illumination circuit.

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berkeman

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Or else maybe he means that he has the LC circuit you describe, but then he really does short out the inductor when it has maximum current going through it. This is a pretty benign short, since the voltage across the inductor is zero when the current is not changing (at the top of its sine wave current waveform). With that shorting wire in place across the inductor (and across the capacitor too, since the L and C are connected together), the current in the inductor will keep circulating through the inductor and wire, and will ramp down slowly with the L-R time constant, where the R is the resistance of the inductor windings and the shorting wire.SGT said:

Since the voltage in the inductor is [tex]L\frac{di}{dt}[/tex], making [tex]dt = 0[/tex] causes the voltage go to infinity.

A physical inductor has associated to it a winding resistance and a winding capacitance, so in practice you will have a high frequency, high voltage damped oscillation.

If the amplitude of the voltage is high enough, the air in the open gap can be ionized and a spark appears. This is observable when you switch off a fluorescent illumination circuit.

Open circuiting a current-carrying inductor is definitely more interesting than shorting it out. :rofl:

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