A metal sphere centered at the origin has a surface charge density that has a magnitude of 24.1 nC/m2 and a radius less than 2.00 m. At a distance of 2.00 m from the origin, the electric potential is 520 V and the electric field strength is 260 V/m. (Assume the potential is zero very far from the sphere.) What is the sign of the charge on the sphere? Explain.