Mobile Phone Faraday Cage
  A Faraday cage is an interesting physics phenomena where an electromagnetic wave can be excluded from a volume of space by enclosure with an electrically conducting material. The practical application of this in the classroom is to block the signal to a mobile phone by enclosing it in a metal can! The background of the physics behind this is described in some detail followed by a explanation of some demonstrations and experiments which I have used. 
M M J French
physics.pop-ph physics.ed-ph