# Homework Help: Electrical - Missing Capacitor value

1. Dec 2, 2011

### razin

1. The problem statement, all variables and given/known data

Need to find C1
Whats known: VS: 5v rms / C1=? , C2=.0022uf , C3=.0015uf Xc3= 750Ω

3. The attempt at a solution

I would have thought I would need the frequency to start this, but it's not provided.
Stumped on where to even start on this.

2. Dec 2, 2011

### Staff: Mentor

You're given Xc3 and C3. That should let you find the frequency

3. Dec 2, 2011

### razin

Hmm, ok.
This is what I calculated for freq. then, but seems high.
_____1_______
2∏(.0015)(750)

=141471hz

If correct, would give me 513Ω XC for C2.
________1_________
2∏(141.5khz)(.0022uf)

From here I'm lost. How to get C1 still eludes me.

4. Dec 2, 2011

### Staff: Mentor

The frequency is actually much higher than you think! Remember, the capacitor values are given in picofarads.

The scale of frequency won't affect your Xc for C2 though, as long as you've faithfully made the same mistake throughout the calculations! 513Ω is a tad high, but that's attributable to rounding errors (maybe you'll want to keep a few more digits in your intermediate results).

Note that you've also been given a current value. With that current value you should be able to determine the voltage that appears across C3 (and by extension C2 since it's in parallel with C3). What then is the current through C2?