#### mtnkh

##### Newbie level 6

I have a question regarding variable capacitors. Consider there is C(t) and its voltage is V(t). So Q(t) = C(t)V(t) and I = dQ/dt = C(t)*dV/dt + V(t)*dc/dt.

My question: SO for variable capacitor, Impedance(Zc = 1/cjw) cannot be defined. Is it correct? since its differential equations is different. Am I right? if not. Please explain me how we define Impedance for variable capacitors.

Thanks