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Radiowave mediums

  1. May 27, 2009 #1
    Can someone please help me with these questions?

    What things can radio waves pass through?
    Can they pass through walls?
    What things can't they pass through?
     
  2. jcsd
  3. May 27, 2009 #2
    As far as I am aware, wavelengths determine that which they can pass through. For example. microwaves are pretty small, hence the word, micro... and can't pass through the mesh you'll see in your microwave window.. (the gap between each crest)... the odds, likelihood, is that they will hit the mesh and not the glass. Radio, is pretty average, and can be picked up by pot pans. Generally radio waves bounce off everything... x rays and nutrinos with very long wavelengths can pass through stuff... but not lead... most of the time... yeah?
     
  4. May 27, 2009 #3
    Hi there,

    This is a hard one. I guess, you are talking about macroscopic objects or devices. Radio waves being electromagnetic radiation can pass through anything, but everything can stop them. Yeah, that's an answer for you!!!

    Let me explain a bit further. And to do so, I will have to take an atomic point of view of matter. Matter is "filled" with atoms, more or less regularly distributed. Looking at this arrangement from very closely, we would find that there is alot of space between two atoms of matter. Therefore, radio waves will edge their way in this empty space. The wave will continue its route, until it "hits" an atom.

    So from a microscopic point of view, radio waves can only pass through empty space, and atoms will be able to stop them. The more atoms you have in an area, the less chance you give your wave to traverse it.

    Cheers
     
  5. May 27, 2009 #4

    jtbell

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    Staff: Mentor

    Have you ever used a portable radio or TV indoors? Have you ever used a wireless network with the base station or repeater in one room and your computer in another room?

    Walls do attenuate the waves. The amount of attenuation depends on the wavelength, the thickness of the walls, and what the walls are made of. The walls in my house are wood-framing and drywall construction. I can use my wireless network between rooms, and I can use my radio and TV with strong stations (weak distant stations are more difficult). The walls in the building where I work are made of concrete block and wireless networks don't work well or at all between rooms, and a radio works only on the strongest stations.
     
  6. May 27, 2009 #5
    Thanks for the answers.

    But that's what puzzles me.
    Light can only enter our house via windows; not via walls.
    Yet shorter X-rays can pass through us (and ordinary walls I guess?) and radio waves somehow get into a closed house.
    So how do the radio waves bounce into a closed house?

    Sorry jt, just saw your post.
    Sorry, I had to look up the meaning of attenuate.
    That adds to my puzzlement.
    How do shorter X-rays and longer radio waves pass through walls but not visible light which is in between these in wavelength?
     
    Last edited: May 27, 2009
  7. May 27, 2009 #6
    yes, you ask reasonable questions. If you can imagine an open door, with glass uprights and lentil, surrounded with wooden walls and concrete superstructure. Every kind of electromagnetic radiation (all kinds of light) are attacking each mass at the same moment, the dense matter such as concrete are going to reflect most of the radiation where the door will amplify the radiation as it passes though it in the form of positive interference where the waves collide at the same frequency. When the radiation passes through this empty space, there will be positive interference and negative interference as the waves cross each other. The glass will bend this radiation, the door will let it pass, the wood will reflect some, let some pass and the concrete will reflect most. X rays pass through most where the colour spectrum will, as far as we know, always be reflected. Are you asking why glass does not reflect at all?
     
  8. Jun 13, 2009 #7
    Let me try an explanation.

    Different types of radiation interact with matter in different ways. Radiation will only interact with matter that has energy transitions equal to the energy of the radiation. The energy of radiation is proportional to frequency. If there is no available energy transition, then radiation will not interact.

    Visible light is opaque when it is absorbed by an atom's electrons. It transitions the atomic electrons to a higher energy level. If the atom does not have an energy transition equal to the frequency of the visible light, then the matter is transparent.

    Infrared light is absorbed by molecular vibrations, which are only of certain energy transitions. If there is no energy transition equal to the light energy, infrared light will pass through.

    Microwave radiation is absorbed by molecular rotation. Your microwave oven sees water as opaque because the change in energy of water rotation is equal to the energy of microwaves emitted by your microwave. It sees ice as transparent because ice doesn't have this rotational energy level.

    Radio waves, on the other hand, aren't really absorbed by any atomic or molecular energy levels (in a dielectric) as far as I know. That is why it passes through walls.

    It's all physics!
     
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