When a conductor with an open lid is placed in a constant electric field, the electric field within the cavity becomes zero due to the cancellation of electric fields inside the conductor. Although the open lid may allow some charge accumulation at the edges, the net electric field inside remains effectively zero. This principle is consistent with the behavior of Faraday cages, which shield against external electric fields. However, the discussion highlights that the shielding effect may vary with different conductor shapes, as illustrated by the example of a hollow semi-sphere. Overall, while traditional Faraday cages are well-known for their shielding properties, the applicability of similar principles to other conductor configurations remains limited.
