The Faraday cage is named after Michael Faraday, who invented it in 1836. A Faraday cage is a box made of conducting material (e.g. metals) and is used to block out external electric fields. The existing external field exerts a force on the charges of the conducting material. This force produces a redistribution of the charges in the conducting material, causing a certain separation of positive and negative charges. This unbalanced situation results in a second electric field that is directed in the opposite direction of the external electric field, and has the same magnitude of the external electric field. In the box both electric fields cancel eachother (cfr. image).
A well-known example of a Faraday cage is an automobile. If the car is struck by lightning, the biggest part of the charge remains on the metal skin of the car, and little or no electric field is produced inside the car. The phenomenon of blocking external electric fields is also used and needed when no electric interference is wanted (ex. when sensitive electric equipment is used).
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