Roger wrote:

Thanks for the example of P = V(t) * I(t).

I think the example illustrates why the instantaneous power equation P =
V * I that Keith was referencing is not appropriate at all points on the
line. If I understood Keith correctly, he would have calculated 200
watts input for your example (100 volts at 2 amps).

Huh? I calculated 160 watts using P = V(t) * I(t). Why do you think
Keith would have calculated 200 from the same equation? I have no doubt
that his math skills exceed mine, and I used nothing more than complex
arithmetic and high school trig.

I calculated power at the input end of the line, but I can calculate it
from the same equation P = V(t) * I(t) at any point on the line, and
will get exactly the same result. At what point(s) do you think it's not
"appropriate" to use?

Roy Lewallen, W7EL