  In an ordinary time-varying capacitor, there is debate whether a time-domain
multiplication or a time-domain convolution of capacitance and voltage
determines charge. A time-varying capacitor in parallel with a resistor was
implemented by a motor-driven potentiometer and op-amps. The response matched a
power-law function over about two decades of time, and not an exponential, for
several sets of parameters. This confirms the time-domain multiplication model.
This result is the opposite of that obtained for a Constant Phase Element (CPE)
in its common time- and frequency-varying capacitor interpretation. This
demonstrates that a CPE is fundamentally different from an ordinary time- and
frequency-varying capacitor.
