If you're inside a Faraday cage, you are supposed to be electromagnetically isolated from the outside. But I was able to make a phone call and even use Wi-FI on a plane. Why doesn't this violate the laws of physics?

  • 4
    $\begingroup$ are you talking of an airoplane? it has antennas outside its "faraday cage". also for mobile, it can pick the inside signals and with wiring use antennas to communicate with the outside world, and bring in wireless signals with a corresponidng antenna inside $\endgroup$
    – anna v
    Jul 19, 2018 at 8:57
  • $\begingroup$ When you used wifi, are you sure the base station was outside the plane? $\endgroup$
    – The Photon
    Jul 19, 2018 at 17:38

1 Answer 1


Simply because you are not inside a perfect Faraday cage. EM waves can propagate through the windows and various holes of the cabin.

Which frequencies propagate depends by the size of the windows. You can think to each window as a waveguide connecting to the outside. The propagation through the windows depends by the 'waveguide' cutoff frequency. Since the frequency of cell phones is of hundreds of MHz, apertures of tens of cm let the EM waves propagate through.

See https://en.wikipedia.org/wiki/Waveguide#Propagation_modes_and_cutoff_frequencies

Estimate the exact cutoff frequency depends upon the geometry of the windows.


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