Art of Electronics 3rd ed. 1.7.1 Frequency analysis of reactive circuits
green: current I(t)
blue: voltage
Current as a function of time:
I(t) = C*dV/dt = C*ω*V₀*cos ωt
The phase of current leading the input voltage by 90°
Amplitude only: I = V/ (1/ωt)
where ω = 2*π*f
R = 1/ωC
For example a 1μF capacitor put across the 115V (rms) 60Hz powerline draws a current of rms amplitude:
I = U/R
I = 115V / (1/ 2*π * 60 * 10⁻⁶F) = 43.4mA (rms)
