On Jun 5, 9:29*am, Cecil Moore wrote:
On Jun 4, 5:39*pm, Keith Dysart wrote:

So are you really prepared to give up on P=VI so that energy can be
flowing (i.e. there is power) when the voltage or current is zero?

My apologies for being too terse for you. Please use P(t)=V(t)I(t)

Your equation is for DC power. The equation for net AC power is
P=V*I*cos(theta).

This simplified form works for sinusoids. It is derived from
P(t)=V(t)I(t),
but loses information since the result is just the average value.

Since, for a pure standing wave, the net voltage is
always 90 degrees out of phase with the net current, the net power at
ALL points is zero, not just at the I=0 point. cos(theta) is ALWAYS
zero for a pure standing wave whether I=0 or not

Well so it appears when you use the simplified form, but if you use
P(t)=V(t)I(t), that is, do a bit of time domain analysis, one finds
that energy is moving back in forth within the line. It only does
not cross those points where V or I is always 0.

- so your argument is moot.
For a pure standing wave, P = V*I*cos(theta) is ALWAYS zero. I
or V going to zero cannot make it more zero than it already is.

The difference will be easy to see if you analyze in the time domain
rather than just using the averages.

....Keith