Why can't I use a mobile phone on the Underground? © Getty Images

Why can’t I use a mobile phone on the Underground?

High-frequency signals, like the ones used by mobile phones, are easily blocked by thick barriers of concrete or soil.

Asked by: Sam Short, Enfield


Mobile phones operate on a high-frequency signal that’s easily blocked by soil or concrete. Signals further down the spectrum travel relatively unhindered. For instance, medium wave radio stations can be heard in motorway tunnels, while higher-frequency FM stations cut out. Mobile phones operate in an even higher range and can’t work underground without a prohibitively large networkof repeaters to maintain consistent coverage.


Subscribe to BBC Focus magazine for fascinating new Q&As every month and follow @sciencefocusQA on Twitter for your daily dose of fun science facts.