The phenomenon in which a certain region of space is protected from the electric field is called electrostatic shielding. Consider a conductor of any shape having a cavity inside it as shown in the figure. Let +q be the charge on the conductor. Draw a Gaussian surface just around the cavity inside the conductor as shown by dotted closed lines.
From Gauss's theorem
\(∮ \vec E. \vec{dS} = \frac{q}{ɛ_o}\)
Since charge inside the conductor is zero i.e. q = 0
∴ \(∮ \vec E. \vec{dS} = 0\)
or \(\vec E = 0\)
or E = 0
i.e. electric field inside the cavity of a conductor is always zero.
Importance:
(i) In a thunderstorm accompanied by lightning, it is safer to be inside a car or a bus rather than near a tree or on the open ground.
(ii) In electronic devices, certain circuits or components are shielded by covering them with metal shields.
