# Homework Help: LRC series circuit.

1. Mar 1, 2006

### jakeowens

A L-R-C series circuit contains a 1x10^-6 F capacitor, a 7.00 mH coil and a 90 ohm resistor. What is its resonant frequency?

For this one I used the formula for capacitive reactance.

Xc=1/2pi*fC

After doing some algebra i isolated the frequency giving me :

f=(1/Xc)/2pi*C.

So i substitute all my values giving me:

f=(1/90)/2pi*1x10-6F...

The answer i get seems really wrong. Did I use the wrong formula?

Should i have used XL=2pi*fL?

I'm really at a loss for what to do with this problem

any help would be appreciated

2. Mar 1, 2006

### Staff: Mentor

The resonance comes about because of the two energy-storing elements, the inductor and the capacitor. To figure out the resonant frequency, concentrate on the L and the C.

Hint, where are the reactance (complex impedance magnitude) of the inductor and capacitor equal?

3. Mar 2, 2006

### physicsprasanna

right.... and one more thing ... you seem to have substituted 90 for Xc ...
90 ohm is the resistance of the resistor given.. But Xc is the reactance of the capacitor ...

they are two different things

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