Source: High school physics (Chinese)
Problem Sets:
Problem
A charged body is brought close to a conductor shell.
- Does the charged body alone produce zero electric field inside the cavity of the conductor shell?
- How is the electrostatic shielding effect of the conductor shell manifested?
(1) No --- the charged body alone produces a non-zero field inside the cavity. (2) Induced charges on the conductor surfaces produce a counter-field inside the conductor that cancels the external field, leaving the cavity field-free.
The charged body alone (in vacuum) produces a non-zero field everywhere in space, including inside the cavity of the shell. The shielding arises in electrostatic equilibrium: the conductor's free charges redistribute, and induced charges on its outer and inner surfaces produce, inside the conductor, a field that exactly cancels the external charge's field. Provided no charges sit inside the cavity, the cavity therefore remains field-free regardless of what is placed outside. This cancellation by induced surface charge is the essence of electrostatic shielding.