Faraday cage
A conducting shell shields its interior from external electric fields. Free charges on the conductor redistribute until the internal field cancels perfectly. Field lines bend around the cage, induced surface charges accumulate, and the interior stays field-free — no matter how strong the external field.
Michael Faraday demonstrated in 1836 that a conducting enclosure blocks external static electric fields. The mechanism is simple: free electrons on the conductor move in response to the external field until they create an equal and opposite field that perfectly cancels it inside.
This simulation models the cage as a set of conducting point charges that are free to redistribute along the cage boundary. An iterative relaxation method finds the equilibrium charge distribution where the total internal field approaches zero. The induced charges accumulate on the side facing the field (positive) and the opposite side (negative), creating a dipole layer that shields the interior.
The shielding is imperfect for sparse cages — with few conductors, field leaks through the gaps. As you add more conductors, the gaps shrink and the shielding improves. A continuous conducting shell would produce perfect shielding.
Faraday cages are everywhere: microwave oven doors, MRI rooms, coaxial cables, and the metal fuselage that protects airplane electronics from lightning.