John said:
I'm trying to get a feel for why the radio
goes out when I stand in certain parts of
the room, mostly near the large window. I
thought, well if radio wave are like light
then maybe they are shining through the
windows and maybe I'm casting a shadow.
Interference. Have you ever seen a laser
speckle pattern? The same thing happens on
a larger scale anywhere you have radio waves
bouncing around in an enclosed space (i.e.,
a room). There are strong spots where the
various reflection paths are in phase so
that they reinforce one another, and there
are weak spots where they are out of phase
and they cancel out.
You are not casting a shadow. You *WOULD*
cast a shadow (a faint one) if you were out
in space, and the transmitter were far away.
You don't cast a shadow in your room for the
same reason you don't cast a shadow on the
ground on a cloudy day. On a cloudy day,
the light is coming from all directions.
The radio waves in your room are coming from
all directions too because they're bouncing
off the walls of your house and all of your
neighbors' houses, nearby hills, etc.
I'm having trouble seeing how this light
can shine through walls merely because
there is more of a delay between one pulse
of energy, a wave, and the next.
The wave crests are not "pulses of energy."
I don't know what they are. I don't know
if anybody *REALLY* knows what they are.
All I know, and all that most garden-variety
physicists know is that whatever electro-
magnetic energy is, it seems to obey (ON
AVERAGE!) the same mathematical laws that
govern waves like on the surface of a pond.
My understanding of why certain wavelenghts
pass through some materials and not through
others is pretty weak, but I know that it
has to do with the fact that electrons in
the material are confined to certain "energy
levels," and they interact with photons of
different wavelengths (i.e., photons of
different engery) only when the difference
between two allowable energy levels for the
electron is compatible with the photon
energy.
What is "allowable" and what is not
allowable depends on the the atoms in the
material and on the way they bond to one
another, and it's so far over my head it
isn't funny.
I know that from watching welders that
high frequency light casts sharper shadows
at a further distance than regular light...
but I'm not certain why that is
Ah, shadows again.
That's a simple geometry problem.
A welder's arc is a very compact, very bright
source of light. A compact source casts
sharper shadows than a larger source, and the
fact that the source is very bright makes the
shadow very noticible.
-- Jim L.