Original poster: "Antonio Carlos M. de Queiroz" <acmdq@xxxxxxxxxx>
Tesla list wrote:
Original poster: Ed Phillips <evp@xxxxxxxxxxx>
"Right; I was thinking about the hot resistor in the RLC circuit. If
you
have an ideal LC resonantor with zero bandwidth and infinite Q, and then
you wiggle the capacitor plates to add some FM, the losses are still
zero
so the Q is still infinite.
This depends on how the capacitor changes. There is no loss if the
capacitance changes instantaneously when the capacitor voltage is
zero. If there is some charge in the capacitor, a decrease in the
capacitance increases the energy. An increase in the capacitance
decreases the energy. It's then possible to increase continuously
the energy in the circuit by decreasing the capacitance at any moment
and increasing the capacitance back at the zero crossings of the
capacitor voltage. The opposite operation drains energy from the
circuit. There is no resistor in this circuit. Energy goes in and
out in the force required to move the capacitor plates against
the electrostatic force between them.
Something similar can be obtained with a time-varying inductor.