Richard Harrison wrote:
For the power sine wave, though the fact that a minus times a minus is a
plus results in 2x the voltage frequency, dP/dt=0 at maxima.

Alternatively, from amplitude modulation, the product of two sine waves
produces a sum and difference frequency. When the two sine waves have
the
same frequency (as they due for the voltage and current contributing to
the power), the result is a double frequency sine wave and a 0 frequency
difference which is the DC or average power.

A question raised in this thread is, how can energy, which is joules per
second times seconds, be zero when the number of seconds is zero? The
answer seems obvious. Zero times anything is zero.

Exactly. And when the voltage or current is always zero, so must be the
power.

....Keith