Friday, 22 October 2010

Faraday's Cage

Faraday cage, after the English scientist Michael Faraday,  is a metallic enclosure that prevents the entry or escape of an electromagnetic field. It lets electric charges travel on the outside of it, while the electric field effects are cancels out in the centre of it, leaving the inside like the eye of the storm. It is widely used to for protecting electronics from lightning storms. An ideal Faraday cage consists of an unbroken, perfectly conducting shell, in reality this is impossible to achieve, however a fine-mesh copper screening is a good solution. Ideally the cage should also be connected to an earth ground.

You have probably heard of the classic tip to sit in your car for protection during lightning storms, since cars are Faraday cages. However, they are not very good Faraday cages since they are not unbroken (windows, etcetera) and since they are isolated by the tires and thus not connected to an earth ground. Having a car made with fiberglass or an convertible would further decrease the effect. In newer cars the many electronic connection going into the interior of the car, could also be a problem. If you use a car as a Faraday cage, make sure you are not touching the outer walls or anything that is conducting electricity that is connected to them. 

Some claim the radiation from cell phones will be trapped inside the car, by the same principles, thus increasing its harmfulness. This view is however widely disputed, and seem to be mostly spread by people basing their business helping against it and less serious actors.

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