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Homework Help: Series RLC circuit

  1. May 5, 2015 #1
    1. The problem statement, all variables and given/known data
    Given a series RLC circuit:

    R = 10 Ω
    L = 0.1 H
    C = 2 μF
    Power Source: V = 5sin(500t)

    If you could change the capacitance what C would you select so Vrms across the capacitor and inductor is zero?

    2. Relevant equations
    ω2 = 1/LC

    3. The attempt at a solution
    My instructor's solutions say to use above equation for resonance frequency to input ω=500 (given from V) and
    L = 0.1 H and then solve for C, yielding 0.00004 F.

    This makes no sense, could someone explain it to me?
  2. jcsd
  3. May 5, 2015 #2


    User Avatar
    Science Advisor

    Remember: The voltage across the inductance is 180° out of phase with respect to the voltage across the capacitor (jωL vs. 1/[jωC]).
  4. May 5, 2015 #3
    Ok, I think I get it.

    Given a phaser representation, tan(φ) = (XL - XC) / R

    So tan(180) = 0 ⇒ XL = XC which is resonance.
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