Where's the energy? (long)
Mike Monett wrote:
There is a bad mixup here. He claims:
"Note especially that the electric and magnetic fields are not in
phase with each other, but are rather 90 degrees out of phase. Most
books portray these two components of the total wave as being in
phase with each other, but I find myself disagreeing with that
interpretation, based on three fundamental laws of physics"
He claims the E and H fields are in quadrature. I claim he is wrong.
If the E and H fields were in time quadrature, you'd have a power
problem.
I believe that is what I tried to tell him. He bases his argument on
the following:
1. "The total energy in the waveform must remain constant at all
times."
Not true. It obviously goes to zero twice each cycle.
2. "A moving electric field creates a magnetic field. As an electric
field moves through space, it gives up its energy to a companion
magnetic field. The electric field loses energy as the magnetic
field gains energy."
Only if the environment is purely reactive. Not true with a pure
resistance.
3. "A moving magnetic field creates an electric field. This is
Faraday's Law, and is exactly similar to the Ampere-Maxwell law
listed above. A changing magnetic field will create and transfer its
energy gradually to a companion electric field."
Regards,
Mike Monett
Mike,
This concept is not unique to the web site you referenced. I have seen
several other debates about the same thing.
One thing that is missed in this simple analysis is a consideration of
the uncertainty principle. Heisenberg proposed in 1927 that it is not
possible to simultaneously know the value of position and momentum to
arbitrarily high accuracy or to know the value of energy and time to
arbitrarily high accuracy.
The uncertainly for energy and time is given as delta E x delta t must
be greater than or equal to h-bar, which is Planck's constant divided by
2 pi.
The energy of a photon is h-bar x omega, where omega is the angular
frequency of the photon.
In order to declare a violation of energy conservation in the wave
example above, one would need to examine the energy at time intervals at
least as short as half the wave period. Guess what, the uncertainty
principle says that if we attempt to do so we cannot determine the
energy to the accuracy required in order to claim a violation of energy
conservation. Note carefully that "determine" does not mean we must
actually measure the energy. The energy cannot even be defined more
accurately than the limit imposed by the uncertainty principle.
One way to look at this is that during the interval over which one might
try to claim a violation of energy conservation the energy is in a
virtual state. As you may know, this sort of consideration is everywhere
when one delves into atomic scale and quantum mechanics.
73,
Gene
W4SZ
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