Geez, this question makes me feel like I'm on "Who want to be a millionaire"!
Brain should have provided multiple choices for his two questions.
George, good anaolgy re the pumpkin. Here is some other stuff I remember
from my hated electric field classes some 40 years ago. If the radiator is a
point
source in space, and the energy is equally distributed in a spherical pattern,
the
energy at any point in space drops off as the cube of the distance from the
source.
If the radiator is an infinite line, the energy drops off as the square of the
distance
from the source. If the source is an infinite plane, the energy remains the
same
regardless of the distance from the plane. Are these right?
Now to the tough part about RF travelling in space. Note that all energy we
receive from the sun comes in some form of electromagnetic energy, ranging
from frequncies which give us light, to infrared which gives us heat, in
addition
to all kinds of non-structered RF signals.
Doesn't electromagnetic energy depend on the sequential exitation of electrons
from one adjacent molecule to another to "travel" anywhere? It is my
understanding
that space is not a vacuum, but merely a lower pressure than that here on earth.
The
molecules may be further apart (less dense), but are still out there. The only
TRUE
vacuum I know of is what they call a "black hole" in space, which literally
sucks all
nearby matter into it......but this is still a theory.
Brain, the RF energy, or any other part of the EM spectrum, travels through
space
just as in the water you mentioned, only with different molecules, and spacing
of
same.
These are my FINAL answers. Did I win anything, or must I go home a loser?
George
george_tang%dell....@interlock.lexmark.com on 11/30/2000 03:56:59 PM
Please respond to george_tang%dell....@interlock.lexmark.com
To: brian_kunde%leco....@interlock.lexmark.com,
emc-pstc%majordomo.ieee....@interlock.lexmark.com
cc: (bcc: George Alspaugh/Lex/Lexmark)
Subject: RE: How does RF travel through outer space?
We all just carved pumpkins not too long ago. We can use pumpkins to
explain one of these questions. If you put a 5 watt light bulb at the
center of your carved pumpkin, then each square inch of the internal pumpkin
surface gets the amount of light energy given by the expression:
5W / (internal surface area of pumpkin) = light energy per square inch
Now you move your light bulb to a bigger pumpkin and do the same
calculation. You find that each square inch of your bigger pumpkin gets
less light energy due to a bigger surface area. This is why RF signals drop
off at the rate of 1/distance squared, since the pumpkin surface area is
proportional to the square of the radius. Light is simply a higher
frequency emission than RF, but the same concept applies.
As far as "How RF travel through vacuum," you can think of it this way: RF
is composed of electric field and magnetic field. Electric field is simply
the attraction force between the positive charges and the negative charges.
And magnetic field is the interaction between 2 current loops. It is not
hard to imagine that refrigerator magnets will work in vacuum or protons and
electrons will attract in outer space. RF is simply the electric and
magnetic fields changing polarity at a very rapid rate.
George
-----Original Message-----
From: brian_kunde [mailto:brian_ku...@leco.com]
Sent: Thursday, November 30, 2000 12:51 PM
To: emc-pstc
Subject: How does RF travel through outer space?
Hello,
I'm sorry if this is too simple of question... "How does RF travel through
outer
space?".
I will be teaching a class in which this question will come up. I want to be
prepared with all the basic science behind this principal. I need an
explaination that is simple and easy to understand.
People seem to have no problem understanding how waves can travel through
mass
such as a body of water but can not understand how it can travel where there
is
no mass. I also understand that there is a lot of debate over how Light
travels
through space (photons and all).
Also, I understand that RF signals degrade at a rate of 1/distance(squared).
What force is causing this attenuation?
Try to keep it simple for my audience it not all that technical. Appreciate
the
help. Please forgive any improper punctuation or word misuse.
Brian
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