Gauss law. Compute the total charge inside the "sphere" at the given radius r. Note, inside the sphere, you only have a fraction of the total charge.
E=kQ/r^2
A spherical conductor has a radius of 14.0 cm and charge of 26.0 µC. Calculate the electric field and the electric potential (a) r = 10.0 cm, (b) r = 20.0 cm, and (c) r = 14.0 cm from the center.
3 answers
The electric potential inside the sphere will be the same as it is on the surface so a=c. You can use the equation V=q/(4pi*8.89e-12*r) to find the potential where r is the radius from the center if that radius is greater than or equal to the radius of the sphere and q is the charge on the sphere. The electric field inside the sphere is zero. You can use the equation you supplied to find it elsewhere. Note this will only work for an enclosed sphere, meaning no holes in it.
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