Resonant frequency problem (basic electronics)

Discussion in 'Homework Help' started by bnixdo, Mar 4, 2013.

  1. bnixdo

    Thread Starter New Member

    Mar 4, 2013
    Hey everyone, this is my first post here, but I'm a longtime reader.

    Here's the question:

    A series circuit contains L = 159 μh; C = 159 pf; R = 20 Ω. The supply voltage is 100 volts.
    a) Calculate the resonant frequency.
    b) Calculate the circuit impedance Z at resonance and for frequencies of 25, 50, 100, and 200 kHz above and below resonance. Indicate whether these impedances are resistive, inductive, or capacitive. Plot a curve of Z versus f.

    Now I started with part a) by using fo = 1/(2π√(LC)), substituting in 159x10^(-6) for L and 159x10^(-12) for C. This gave me an answer of:

    fo = 1000000 cycles

    ^^Is this correct?^^

    Now if it is, for the second part, do I just use the formulas for inductive reactance and capacitive reactance (XL = 2πfL ; XC = 1/(2πfC) and substitute in the L and C values for each +/- of frequencies, then compare and see if XL > XC (inductive impedance) or if XC > XL (capacitive impedance), etc?

    Thanks a lot.
  2. JDT

    Well-Known Member

    Feb 12, 2009