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While determining the electric field in a Non-Conducting Sphere using Gauss's law,why the positive charges are considered inside the surface,but in determining the electric field in a conducting Sphere,why the positive charges are considered outside the surface?
And,why if any point charge is inside a sphere,the the net electric field is considered zero?
This can be understood by the potential energy. We know that the surface potential energy is less than the volume potential hence the charges wanted to remain in the equilibrium and it is evident from the definition of an insulator the charge does not get distributed.It remains confined in the vicinity of the sphere. It is because the net field of the conductor is zero which dominates the field of point charge.
In a conducting sphere, like charges repel each other - so when there is a net charge, it will all appear on the surface (they try to get as far away from each other as possible). In a non-conducting material, charge will stay wherever you put it - so if you have a solid material with a net charge per unit mass (not sure how you achieved that), it will not redistribute.
If you have a point charge inside a grounded, conducting sphere, the charge will attract equal and opposite charges onto the sphere until the net charge is zero (until that time, there is an external electric field that can pull charge towards the sphere - again, this requires the sphere to be grounded).
If I misunderstood your question please clarify...
