Duduli

Answer:- The maximum electric field that a dielectric medium can withstand without breakdown (of its insulting property) is called it's dielectric strength. The dielectric strength of air is 3×10⁶V/m * Dielectric strength of other medium is greater than that of air.

Reason:- T he capacity of earth is very large.therefore,any amount of charge added to it or taken away from it does not bring about a change in it's potential.therefore,earth is always considered to be at zero potential.look at the mathematical derivation of Earth's zero potential any body connected to earth shall also be at zero potential.the above explanation is the answer to the question why Earth's potential considered to be zero.

Reason:- We know charge resides only on the surface of the conductor so the charge inside the conductor is zero this implaies electric field inside the conductor is zero. i.e

We know conductor is neutral i.e it has equal no. Proton & electron . if we place a charge inside a conductor then it surrounded by their opposite charge to balance that charge and charge inside the conductor became zero and correspondingly their is a charge separation occur in the surface of conductor it is the reason why charge resides only on the surface of the conductor.

We know conductor have free electrons before the equilibrium state. if their is a some potential difference in the surface of conductor then free electrons move their to balance the charge and the  surface became equipotential in the equilibrium state. and it take nano seconds so we say generally surface of conductor is equipotential at equilibrium state.