Naked Science Forum

Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: lunar11 on 09/01/2010 19:54:59

Title: How do radio waves penetrate brick walls?
Post by: lunar11 on 09/01/2010 19:54:59

Gamma rays are very short wavelength EM waves that are very energetic (since E= hf).
Thay are able to penetrate concrete upto a metre in depth.
Radio waves are long wavelength are far less energetic. My question is how do they penetrate brick walls. E.g. I can listen to the radio in a room with no windows, but just solid walls.

Title: How do radio waves penetrate brick walls?
Post by: Soul Surfer on 10/01/2010 00:08:22

Gamma rays penetrate material because their very high energy and short wavelength allows them to pass through the electron cloud of atoms with minimal disturbance other than throwing the occasional electron out of an atom (ionising).  Radio waves penetrate through walls because the material does not absorb them in the same way that glass is transparent to light.  if the wall was conducting i.e. metal, they would not penetrate even weakly conducting (like wet) can have an effect.

Title: How do radio waves penetrate brick walls?
Post by: Geezer on 10/01/2010 06:47:43

Gamma rays are rather "macho". They go straight for it, but they can only go until they hit an obstacle that stops them.

Typical radio waves are less energetic, but more sneaky. They test all possible paths. If there is any way through a wall, they will find it.

Very low frequency radio waves are not very energetic, so they simply go around the wall.

 

Title: How do radio waves penetrate brick walls?
Post by: LeeE on 10/01/2010 14:35:10

I believe that Ultra Low Frequency radio, down to a few hundred Hz, is used to communicate with submerged submarines.  The aerials are very long, of course, and need to be trailed behind the sub, and the bandwidth is very low too, too low for voice communications, and with a data rate of only ~100 bits/second or so.

Title: How do radio waves penetrate brick walls?
Post by: yor_on on 10/01/2010 18:30:31

As Geezer wrote. Long waves diffract  (http://en.wikipedia.org/wiki/Diffraction)around the object instead of penetrating.

But then we have those penetrating too like Radio Waves  (http://www.worsleyschool.net/science/files/electromagnetic/spectrum.html). "These waves are extremely long, anywhere from about 1 metre to as big as 10 kilometres (10,000 m) in length. These waves include AM and FM radio signals, and TV broadcasting signals."

Here is a nice PDF (http://www.paec-soar.org/courses/physics_sl_lesson3_lightenergy.pdf) introducing the concepts.

The reason why those long wavelengths can penetrate when f ex. sunlight (wavelength around 5 x 10-7 meters) can't, seems to be that sunlight is near the same spectrum as matter, although some matter like glass are transparent to light.

Long wavelengths don't recognize matter even though the thicker the mass the more difficulty they will have penetrating. 'wave penetration (http://www.physlink.com/Education/AskExperts/ae175.cfm?CFID=23810584&CFTOKEN=f3ae2d680ac3e9fd-A7A174FE-15C5-EE01-B97CE9CDCA947741)'

But exactly why they can do so?

Long wavelengths have its energy spread over quite a distance so you can't talk about anything ramming its way through matter due to its energy, can you?

It must have to do with the structure of matter, and its own (bound, more or less) wavelengths.

I would really like a good link explaining it too.

Title: How do radio waves penetrate brick walls?
Post by: yor_on on 14/01/2010 17:50:02

Maybe this one can give us an inkling why longer wavelengths can penetrate matter? (http://www.newton.dep.anl.gov/askasci/phy00/phy00890.htm)

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And this one too?
Glass (http://lhs.lps.org/staff/squiring/AppPhysics/SoundLight/WhyGlassTransparent.pdf)