Capacitors:

I'm trying to (fully) understand the principle of capacitor reactance and
high pass filters. I'm having trouble forming a mental picture of how a
capacitor in series with a signal blocks DC and has the lowest impedance
for the highest frequency signals on a voltage and charge-on-the-plate
level. I can understand how a capacitor tied to ground acts as a buffer and
smoothes out high frequencies by averaging the voltage. But I don't really
get how the reverse is true for a capacitor in series with a signal. I can
see how it blocks DC after it is fully charged.

1. How does a capacitor in series work to block a DC signal, but pass a
high frequency signal?
2. If you apply a voltage to a capacitor in series (keeping in mind that it
takes time for the voltage from the power source to rise), I understand
that the current before the capacitor is NON-zero. But what about the
current AFTER (on the other side) of the capacitor? Is it zero or non-zero
(considering that a capacitor is just two parallel plates)?


LC circuits:

1. Consider a parallel LC circuit where the bottom is tied to ground and
the top is tied to a mixed-frequency signal source. I understand that the
parallel LC circuit will shunt all frequencies to ground other than those
around its resonant frequency. After the signal source is removed, the
circuit will eventually lose its energy. How do I make an oscillator out of
such an LC circuit that self-starts (that is, I can simulate in LTSPICE
which doesn't take into account external noise coming into an oscillator
circuit, which is required for some oscillator designs)? I've looked at LC
oscillator circuit types like the Hartley oscillator, but I don't see how
this can self start in theory under ideal conditions.
--=20
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