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