# Resonant frequency problem (basic electronics)

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

1. ### bnixdo Thread Starter New Member

Mar 4, 2013
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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.

Feb 12, 2009
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