On Nov 27, 9:00 am, Cecil Moore wrote:
Jim Kelley wrote:

Cecil Moore wrote:
When an EM wave disappears in its original direction of
travel, what happens to its energy?

What happens to the energy flowing in the lamp cord when you turn out
your desk lamp? :-)

It still exists. It just ceases to be converted to
heat. Do you believe energy can be destroyed?

I am surprised you did not provide a more complete answer to the
question.

When the switch is opened it creates a point with a reflection
coefficient of 1 so
all the energy reaching the point is 100% reflected. This reflected
energy flows
back along the line until it reaches a distribution transformer where
it is
transformed back into the transmission system. It then flows back
along the
transmission system until it reaches the generator (passing through
several
transformers along the way). Of course, there are numerous impedance
discontinuities which make computation more complex and increase the
settling time, but the priniciple of reflected energy still holds.

For convenience, we assume the generator is in a hydraulic plant
which
transforms the energy of flowing water into electricity. This is
reversable, so
the reflected energy is transformed through the generator and turbine
into a
reflected water flow which flows up the penstock. Of course, the net
water
flow is still downhill, but never forget that there is a real forward
flow and a
real reflected flow of water.

It is a bit harder to explain where the reflected ernergy goes in a
thermal
plant because the process does not appear reversible, that is, energy
into
the generator is not obviously converted back into coal. Still, it
must happen
somehow. After all the generator in the thermal plant is fundamentally
the
same as the one in the hydraulic. This leads to the inescapble
conclusion
that there must be reflected coal trains carrying coal back to the
mines,
though the net flow is still from the mine to the thermal plant.

Or is it just possible that some have been overextending a mostly
useful tool?

....Keith