Owen Duffy wrote:
"In the same vein, I saw an assertion without sufficient qualification
that in a transmission line, 50% of the energy is stored/contained in
the electric field and 50% in the magnetic field. Again, general
statements from specified cases."

Now we accept that energy travels a guided path as an EM wave. The
electric and magnetic fields of a wave alternately contain the energy of
the wave. When the electric-field is at its maximum, the magnetic-field
is at its minimum, and vice versa.

The change in one field induces the other field and vice versa. Thus it
is the same energy which is being passed back and forth between both
fields. Therefore, over a prolonged period, 50% resides in each field.

Best regards, Richard Harrison, KB5WZI

(Richard Harrison) wrote in news:11430-461F268E-
:

....
The change in one field induces the other field and vice versa. Thus it
is the same energy which is being passed back and forth between both
fields. Therefore, over a prolonged period, 50% resides in each field.

Richard, "over a prolonged period" is a qualification, and still it doesn't
sufficiently qualify the statement for it to be true.

Owen

Owen Duffy wrote:
"Richard "over a prolonged period" is a qualification, and still doesn`t
sufficiently qualify the statement to be true."

Maybe not the best words, but they are true in the practical case. In an
EM-wave, energy is being passed back and forth netween the electric and
magnetic fields on a periodic basis. At any given instant most of the
wave`s energy may reside mostly in one field or the other at a given
point. Half a cycle nas no practical significance among a million or
more.

Best regards, Richard Harrison, KB5WZI

(Richard Harrison) wrote in news:8451-461F926B-
:

Owen Duffy wrote:
"Richard "over a prolonged period" is a qualification, and still
doesn`t
sufficiently qualify the statement to be true."

Maybe not the best words, but they are true in the practical case. In
an
EM-wave, energy is being passed back and forth netween the electric and
magnetic fields on a periodic basis. At any given instant most of the
wave`s energy may reside mostly in one field or the other at a given
point. Half a cycle nas no practical significance among a million or
more.

Your paragraph above now talks about an EM-wave, my quote was about a
transmission line, let me repeat it to save you going back through the
posts:

"In the same vein, I saw an assertion without sufficient qualification
that in a transmission line, 50% of the energy is stored/contained in
the electric field and 50% in the magnetic field. Again, general
statements from specified cases."

They are not quite the same.

I am not quite sure about the concept of energy at a point that you
discuss, isn't it zero?

Owen

Owen Duffy wrote:
"I am not quite sure about the concept of energy at a point that you
discuss, isn`t it zero."

Not when radio waves are passing by. These waves were likely produced by
electrical energy in a wire somewhere that spread into space around the
wire. Radio waves alternate around a zero value. If symmetrical about an
axis, the waveforms may have zero average values. But that is not how we
value the intensity of a rafio wave. We give it an rms or effective
value which is 0.707 times its maximum voltage profuced during the
cycle.

When speaking of power in an alternating energy value, it is not correct
to say rms power. The effective a-c power value is its average.

I`m not a teacher, never have been, and never intend to be. I think I
got into this discussion by declaring that 50% of the power in a wave
resided in each of its two constituents.

I shall argue no more nor try to explain any more on the topic of radio
waves in this thread. Fred Terman is the master of all masters in my
books and I suggest beginning on page one of his 1955 version of
"Electronic and Radio Engineering" to learn all about "Radio Waves".

From page 1:
"One-half of the electrical energy contained in the wave exists in the
form of electrostatic energy, while the remaining half is in the form of
magnetic energy."

Best regards, Richard Harrison, KB5WZI

Richard Harrison wrote:
Owen Duffy wrote:
"In the same vein, I saw an assertion without sufficient qualification
that in a transmission line, 50% of the energy is stored/contained in
the electric field and 50% in the magnetic field. Again, general
statements from specified cases."

Now we accept that energy travels a guided path as an EM wave. The
electric and magnetic fields of a wave alternately contain the energy of
the wave. When the electric-field is at its maximum, the magnetic-field
is at its minimum, and vice versa.

In addition:
Assuming ideal TEM waves, the B-field (magnetic) is always
orthogonal to the E-field (electric) and both are orthogonal
to the direction of travel. The power associated with the
ideal TEM wave is ExB in watts (no vars). A TEM wave travels
at the c' = c(VF) speed of light and cannot travel at any other
speed. If it slows down or stops, it is not longer a TEM wave
and has necessarily been converted to some other form of energy.
Energy "sloshing" back and forth between reactances is NOT TEM
energy.

The principle of superposition gives us permission to treat
the forward traveling wave and reverse traveling wave separately
and superpose the results. Superposing the results does NOT
change the nature of the TEM waves. The fact that the net total
fields are no longer orthogonal gives the illusion that there
exist vars in the circuit but they are only virtual vars based
on virtual voltages and virtual currents. There are no vars in
ideal TEM waves in ideal lossless purely resistive Z0 transmission
lines. The forward traveling wave TEM fields have no effect on
the reverse traveling wave TEM fields as long as a physical
impedance discontinuity is not encountered.
--
73, Cecil http://www.w5dxp.com