# Homework Help: Frequency where reactence is zero

1. Jul 16, 2008

### kdrobey

1. The problem statement, all variables and given/known data
At what frequency (in Hz) are the reactances of a 58 mH inductor and a 84 µF capacitor equal?

2. Relevant equations
Xl=1/2(Pi)fL
Xc=2(Pi)fC

3. The attempt at a solution[/b
F needs to be the same for both, so i got f by itself in both equations, then had them equal each other, giving me Xl2(Pi)L=1/2(Pi)XcC, but im stuck from there

2. Jul 16, 2008

### Hootenanny

Staff Emeritus

I think you have misunderstood the question. The question wants to know for what frequencies are the reactances the same. In other words, find f such that Xc = Xl.

3. Jul 16, 2008

### kdrobey

so if Xl=Xc, then 1/2(Pi)fl=2(Pi)fC? i tried that then got 1=(2pi fL)*(2pi fC). is that on the right track?

4. Jul 16, 2008

### nicksauce

Yes, now just solve for f.

On a related note, wikipedia tells me
Xc = 1 / (2pi*f*C)
Xl = 2*pi*f*L
Which seems to be the opposite of what you have written, although it should still give the same answer.

5. Jul 16, 2008

### Hootenanny

Staff Emeritus
Looks good thus far .

6. Jul 16, 2008

### kdrobey

got it!!! thanks a lot

7. Jul 16, 2008

### Hootenanny

Staff Emeritus
A pleasure .