Michael Faraday also discovered how you can have an electric field inside a charged conductor. Image you have a room within a room, and the inner room is made completely of metal. You can sit in the inner room with a static charge detector (like an electroscope), and when you charge the surfaces of both rooms, you’ll see sparks flying between the two rooms, but it’s peacefully (electrically speaking) quiet in the inner room. No charge is detected inside the inner room with your electroscope. You can have a bolt of lightning strike the inner room, but it still doesn’t register a charge inside the inner room. Why is that?

The inner room I’ve just described is called a “Faraday Cage”, and it’s often seen at science and magic shows because it absolutely defies common sense, until you really think about it. The inner room is shielding you from electric fields. Any closed conducting surface can be a Faraday cage. By closed, I mean electrically speaking. The cage can be a cage made of bars or chicken wire, but it’s still got to be electrically closed.  During the experiment, you can even run your hands on the inside of the room and still not get a shock from the sparks flying around between the rooms!

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The Faraday cage takes the electrostatic charges and redistributes them evenly around the exterior of the cage. As the cage distributes the charges, it cancels out the electric charges within the interior, making the cage a hollow conductor that has charge only on the external surface.

Click here to go to next lesson on Potential Energy.

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