A Solid Spherical Conductor Has a Radius of 15 Cm $\sigma$

Multiple Choice

A solid spherical conductor has a radius of 15 cm.The electric field 30 cm from the center of this sphere has a magnitude of 800 N/C.What is the surface charge density $\sigma$ on the sphere?

A) 7.1 $\times$ 10^-9 C/m²
B) 1.0 $\times$ 10^-8 C/m²
C) 1.4 $\times$ 10^-8 C/m²
D) 2.8 $\times$ 10^-8 C/m²
E) 1.1 $\times$ 10^-7 C/m²