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How can a mobile phone work inside a closed room with no openings if Line of Sight requires no obstacles between the receiver and transmitters?

I know you may think it's not a Physics question but please answer me if you can.

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  • $\begingroup$ It all depends from the materials used. $\endgroup$ – Matteo Campagnoli Sep 24 '18 at 18:36
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If we're talking about radiowaves they tend to propagate unharmed through walls and such materials. The behaviour of electromagnetics can be modelled to an infinite extent but one can simplify it into there being a relationship between wavelength and how thick walls they can penetrate (of course material also plaus a part).

To summarize, radiowaves travel more or less unhindered through ordinary walls whereas microwaves for instance does not. A line of sight transceiver can be functional even if there are walls and objects in the way, as long as the objects and the walls are transparent to the wavelength in question. Your body and clothes for example are more transparent for xrays then your bones are.

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  • $\begingroup$ Seems right. By the way, Frequency of the waves we are talking about here is around 800-2300Mhz (typical cellular frequencies). $\endgroup$ – ObsessionWithElectricity Sep 24 '18 at 17:58
  • $\begingroup$ So basically these waves just need a straight line path to work? Even if it passes through objects? $\endgroup$ – ObsessionWithElectricity Sep 24 '18 at 17:59
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    $\begingroup$ as long as the obstruction is electrically nonconductive, the waves can travel through it without much attenuation. However, if the wave strikes the obstruction at an oblique angle, part of it gets refracted, and the original beam now becomes two. then behind the obstruction, those two beams can destructively interfere, creating a series of "dead spots" ; radio guys call this "multipath interference". $\endgroup$ – niels nielsen Sep 24 '18 at 18:07
  • $\begingroup$ @ObsessionWithElectricity Depending on the material and thickness of the object, radiowaves are very likely to go through unhindered. Eith shorter wavelengths however, it gets harder and harder for the wavefronts to propagate through objects. 2300Mhz = 2.3Ghz which is very close to a house hold 2.4GHz wifi signal, which we know has some trouble getting through thick walls etc. Topics to read up on would be dielectric losses and conductive losses as well as free space propagation and how electromagnetic waves interact with objects $\endgroup$ – DakkVader Sep 25 '18 at 8:14
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line-of-sight radios work fine inside buildings as long as they are made mostly of wood. They do not when the obstacles are made of things like sheet metal. When radio transmitting frequencies get high enough, however, even things like wood begin to interfere, especially if the wood is live and has significant amounts of water in it.

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  • $\begingroup$ But what about concrete buildings? Basically my question wasn't bothering about materials of obstruction in path. $\endgroup$ – ObsessionWithElectricity Sep 24 '18 at 17:54
  • $\begingroup$ In countries where buildings are made of bricks not wood, signal pass easily. $\endgroup$ – ObsessionWithElectricity Sep 24 '18 at 17:55
  • $\begingroup$ @ObsessionWithElectricity Reinforced concrete (the steel rebar) may be a problem. But sheet metal (the fridge) is worse. $\endgroup$ – Pieter Sep 24 '18 at 22:29

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