Capacitor Short-circuiting

Discussion in 'Homework Help' started by confused, Jan 14, 2004.

  1. confused

    Thread Starter New Member

    Jan 14, 2004
    What does it mean for a capcitor to short-circuit in a circuit that consists of an inductor, a capacitor, and a voltage source (no resistor)?
  2. Battousai

    Senior Member

    Nov 14, 2003
    What you want to do is analyze the effective impedance loading the voltage source.

    The impedance of a capacitor is Z(jw) = 1/jwC
    and the impedance of an inductor is Z(jw) = jwL

    j = (-1)^0.5 and w = frequency in radians/sec

    The inductor and capacitor will either be in series or parallel and using the above equations you can derive an equation for the total impedance loading the voltage source:

    Notice at high frequencies the impedance of a capacitor is 0 (it's a short), and at high frequencies the impedance of a capacitor is infinity (it's open).

    The opposite is true for an inductor.

    Usually an inductor, capacitor and resistor are used in parallel to realize a tank circuit: At the resonant frequency, w = (L*C)^-0.5, the impedance of the inductor and the impedance of the capacitor exactly cancel eachother out leaving only the impedance of the resistor. So what you can make is a filter circuit by appropriatley picking L and C values to allow a certain frequency signal to pass and all other frequencies to be blocked.

    I believe the author of this website has a section on tank circuits, yuo can read that for more information.