Roy Lewallen wrote:
Which definition, yours or the one used by everyone else involved with
electrical circuits? I maintain that power doesn't "flow". Energy flows,
and power is the rate of that flow. The standard definition says nothing
about power "flowing", on a transmission line or anywhere else.

I agree with you. If energy is measured in joules and energy flow
is measured in joules/sec, then it seems to me that if power is
measured in watts, then "power flow" would have the dimensions of
watts/sec or joules/sec^2, which doesn't make any technical sense.

The units of the power-flow vector are watts/unit-area. That's
a value fixed in space-time and that value is not moving.

However, most of my college textbooks from the 50s refer to
"power flow" as do some folks on this newsgroup.

For instance, Ramo & Whinnery talk about an "electromagnetic
theorem concerning *flow of power*".

A transmission line has both distributed capacitance and inductance.
Energy moves between the two. The little program TLVis1 I created and
posted a link to shows this graphically in demo 4, with the energy stored
in the capacitance being in one color and the energy stored in the
inductance another color. You can clearly see how the energy moves back
and forth between the two each cycle.

Now it is my turn to wax technically correct. If the energy in
a standing wave is indeed flowing back and forth between an
inductance and a capacitance, then a standing wave is *NOT* an
EM wave just as the EM energy flowing in a tank circuit doesn't
meet the definition of a wave. Ramo & Whinnery list the properties
of a uniform plane wave: [begin quote]

1. Velocity of propagation, v = 1/SQRT(permeability*permittivity).
2. No electric or magnetic field in direction of propagation.
3. Electric field normal to magnetic field.
4. Value of electric field is the intrinsic impedance (ii) times
the magnetic field at each instant.
5. Direction of propagation given by direction of ExH.
6. Energy stored in electric field per unit volume at any instant
and any point is equal to energy stored in magnetic field per
unit volume at that instant and that point.
7. Instantaneous value of Poynting vector given by
E^2/ii = ii*H^2, where E and H are the instantaneous values of
total electric and magnetic field strengths. [end quote]

A standing wave doesn't satisfy any of those properties.
--
73, Cecil http://www.w5dxp.com