To determine the potential at any point outside the sphere, the charge should be assumed to be concentrated at the centre of it.

Therefore the potential at a point, S metres from the centre of the sphere having the charge Q coulombs,

=  Q     = 9 X 10⁹ Q  volts
 4π∈_o S              S

To determine the potential at the surface of sphere of radius r metres substitute S = r i.e above expression for potential

Potential at eh surface of a sphere of a radius r metres and consisting of charge Q. V = Q  = 9 X 10⁹  Q
                                                                                                                           4π∈_o S            r
volts.

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