This question harkens back to the days when it was supposed that there was some "ether" or etherial material, through which EM waves must propagate. You can still hear people occasionally say that a message arrived "through the ether." It was a (logical at the time) extrapolation from sound waves, which by their nature need a carrier medium. So, nobody should feel inadequate for thinking that such an ether must exist. Prestigeous scientists of the last century thought exactly the same thing. It was was only the hard evidence of experiment that proved otherwise.
The reality (arrived at only after significant experimentation) is that electric and magnetic fields (which are really just representations of observable phyisical attractions and repulsions) simply are. They exist regardless of the material (or vaccum) through which they propagate. Existence in a vaccum is in fact their purest manifestation. The presence of material will in fact alter or warp the fields through dielectric or magnetic permeability (molecular sized electric dipoles or electron spins which in effect create their own fields). Hope this helps. Paul O'Shaughnessy Affymetrix, Inc. -----Original Message----- From: [email protected] [mailto:[email protected]] Sent: Thursday, November 30, 2000 3:57 PM To: [email protected]; [email protected] 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:[email protected]] 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 ------------------------------------------- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. To cancel your subscription, send mail to: [email protected] with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Jim Bacher: [email protected] Michael Garretson: [email protected] For policy questions, send mail to: Richard Nute: [email protected] ------------------------------------------- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. To cancel your subscription, send mail to: [email protected] with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Jim Bacher: [email protected] Michael Garretson: [email protected] For policy questions, send mail to: Richard Nute: [email protected] ------------------------------------------- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. To cancel your subscription, send mail to: [email protected] with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Jim Bacher: [email protected] Michael Garretson: [email protected] For policy questions, send mail to: Richard Nute: [email protected]
