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Homework Help: Effective Voltage in series RLC circuit

  1. Nov 20, 2011 #1
    1. The problem statement, all variables and given/known data
    Given a series RLC circuit with a sinusoidal voltage input, find the effective voltage across each element.


    1) If the effective value of the source voltage is 1 V, the effective value of the current is 1 amp.
    2) i(t) lags v(t) by 45 degrees
    3) L=1H
    4) w=2 rads/sec

    2. Relevant equations
    Veff = [1/T * ∫ v^2(t) dt] ^ (1/2)
    Ieff = Im/√2
    Veff = Vm/√2

    3. The attempt at a solution
    Based on the information I know that:
    v(t) = Vmsin(2t)
    i(t) = Imsin(2t-45)

    Not exactly sure where to go from here especially since R and C aren't given, but I'm assuming you don't need these values or can find out based on the information already given.
  2. jcsd
  3. Nov 20, 2011 #2

    rude man

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    For an RLC series circuit, what is the expression for the angle between current i and applied voltage V? Be careful of sign (i leads vs. lags V).

    For same circuit, what is the expression for the magnitude of impedance (V/i)?

    2 equations, 2 unknowns, solve.
  4. Nov 20, 2011 #3
    Ok I'm assuming each equation will be a function of R, L, and C? So I could solve for R and C?

    From there do I just find the voltage/current as a function of time across each element and solve from there?

    What is the significance of the first given statement?
  5. Nov 20, 2011 #4

    rude man

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    |V/i| is one of your two equations. It's the magnitude of impedance of the circuit, i.e. without regard to the phase angle between V and i.
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