On Jun 5, 12:08*pm, Keith Dysart wrote:
On Jun 5, 7:42*am, K1TTT wrote:

On Jun 5, 12:19*am, Keith Dysart wrote:
That is, the power (i.e. energy flow) at any instant in time is the
voltage at that time times the current at that time. If, for all time,
the current or voltage is 0, then so is the energy flow.

...Keith

right, and this brings up another key error that a detailed look at
standing waves points out. *go look at one of the animations of
standing waves and you will note that in each cycle they go from tall
peaks to a flat line and then back to peaks. so if you use p=vi *what
is the energy in the line when either field is zero from end to end?

We need to carefully understand the meaning of the words. Power is
energy
that is moving; the SI unit is the watt or joule per second. The unit
for energy is the joule.

When the voltage or current is zero everywhere, there is no power,
that
is, no energy is moving. The energy is stored on the line where it
happens
to be. As the voltage or current rises again from zero, the energy is
now moving in the direction opposite to the direction it was moving
before
the line was zero everywhere. At a point where the voltage or current
is
always zero, no energy moves. The energy sloshes back and forth
between
the points in the line that it never crosses.

it just alternates between the electric and magnetic fields

This is true, but the energy also changes location as it does this,
leading
to energy flow (or power), but the energy does not cross any point
where
the voltage or current is always zero.

When the current everywhere is zero, no energy is flowing, and the
energy
is stored as voltage in the capacitance of the line. And those
voltages are
at maximum and will soon begin to decrease as the energy begins to
flow the
other way.

Similarly, when the voltage is zero everywhere, the energy is stored
as
current in the inductance of the line.

...Keith

sorry, you are of course correct that there could still be energy
stored in the fields when the instantaneous power is zero... wrote
that before having enough caffeine this morning.