When we find electric field for a conductor having closed surface, then we take charge inside conductor zero, because in conductor charge comes on surface due to force between charges. This is what I have studied.
But for an ideal conductor, permittivity is infinite so electrostatic force must be zero inside conductor, then how charges come on surface?
The electrostatic field is zero AFTER equilibrium is established (after the internal E-field cancels the external E-field.)
Remember the equation that describes the introduction of charges at some interior point of a given material:
What it means is that any charge introduced at the interior of the conductor will decay immediately and appear on the the surface.
Stated in other way, if some charges are introduced in the interior of a conductor, the charges will move to the surface and redistribute themselves quickly in such a manner that the field inside the conductor vanishes.
But for an ideal conductor, permittivity is infinite so electrostatic force must be zero inside conductor, then how charges come on surface?
Consider a physical conductor where the mobile charge, assuming an initial configuration of mobile charge inside, relatively quickly respond to the electric field within, rearranging in a such a way that the electric field inside the conductor (effectively) vanishes.
In a physical conductor, due to a variety of factors, this rearrangement does not occur instantly; there is a characteristic relaxation time \$\tau_e\$ associated with conductors.
However, we can imagine 'taking the limit' of these factors in such a way that the relaxation time goes to zero to arrive at the abstraction of an ideal conductor.
Then, it's easy to see why we say the permittivity is infinite - the charge can redistribute instantaneously such that the field inside the conductor is zero regardless of the external electric field.
