how do i calculate an unknown capacitor in series?

Question

I know one capacitor is-C1= 0.033uF the Xc = 8000 Ohm's and the frequency is 1kHz also the Vrms in is 1.42V (4.02V peak to peak) with one resistor 4.7kOhms.The resistor is first in theseries circuit then Ci then C2.

Answer 1

Sounds like you either left something out or gave more information than needed, because if you're trying to find the capacitance, but give frequency and Xc, that's all you need.

Xc = 1/(2pi * f * C) so,
C = 1/(2pi * f *Xc) so,
C = 1/(2pi * 1K * 8000) = @200uF

If this isn't right, then try to be a little more thorough when typing out the question.

Answer 2

You have the two essential pieces of information, Xc and the frequency.

You know the formula for calculating Xc, don't you?

Subsitute the two knowns and solve for C.