Finding the radius of a charged metal sphere

[Jimmy25]

Homework Statement

A metal sphere centered at the origin has a surface charge density that has a magnitude of 24.6 nC/m2 and a radius less than 2.00 m. At a distance of 2.00 m from the origin, the electric potential is 540 V and the electric field strength is 270 V/m. (Assume the potential is zero very far from the sphere.)

1. What is the radius of the sphere?
2. Is the charge on the sphere positive or negative?

Homework Equations

The Attempt at a Solution

I found the radius as 0.623 m but how do I determine the sign of the charge on the sphere?

 

[payumooli]

shouldn't the electric field tell you the charge of the particle creating it