Calltrex wrote:

"Cecil Moore" wrote:
Sometimes voltage and current have the same signs and sometimes
they have opposite signs.

That 'sometimes' opposite is extremely important in my eyes.

I should have said: "Sometimes voltage and current
*envelopes* have the same signs and sometimes they
have opposite signs." The voltage snapshot is at
t=0. The current snapshot is at t=90 degrees, i.e.
they do not occur at the same time.

Let's see if I can say it a different way.

When the current standing wave envelope is a cosine wave
at its maximum, the voltage standing-wave waveform is zero.

When the voltage standing wave envelope is a sine wave at
its maximum, the current standing-wave waveform is zero.

The graphs of voltage and current envelopes at which you
are looking do *NOT* occur at the same time. There is nothing
except confusion to be gained from assuming they occur at the
same time - since they *NEVER* occur at the same time.

For V*I to be meaningful in reality, they have to occur
at the same time. When the voltage envelope is at its
maximum, there is zero energy in the magnetic field.
When the current envelope is at its maximum, there is
zero energy in the electric field.
--
73, Cecil, IEEE, OOTC, http://www.w5dxp.com