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series LC questions

Discussion in 'Electronic Basics' started by PDRUNEN, Jan 26, 2005.

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  1. PDRUNEN

    PDRUNEN Guest

    Hi Group,

    When the jwL is equal to -1/(jwc) at Frequency Fres for the series LC, the
    circuit is a shunt and become a "short" to RF at the resonate frequency.

    Given that the Inductor is on the top side and the cap is on the bottom side
    with one end tied to ground potential.

    If the sine source is 50Vrms with 1 ohm output and the reactance are j50 and
    -j50 and I measure the voltage across the cap, would it be Zero Voltage or 50
    volts are many takes greater than 50 V?

    Tnx de pdrunen
     
  2. Andrew Holme

    Andrew Holme Guest


    I think you mean 50Vrms with 1 ohm output impedance :)

    Current = Voltage / Impedance

    I = 50 / (1 + j50 - j50) = 50/1 = 50 Amps RMS

    Voltage = Current * Impedance

    Voltage across capacitor = 50 * -j50 = -j2500

    i.e. 2500V RMS 90 degrees out of phase with the current.

    The voltage across the inductor is the same magnitude, but 90 degrees
    out of phase the other way (+j2500)

    The voltages across L and C are 180 degrees w.r.t each other - so they
    cancel.
     
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