Final answer:
The electric field inside a hollow conducting sphere with an excess charge is 0 N/C, due to the properties of conductors and Gauss's law.
Step-by-step explanation:
The question pertains to the electric field inside a conducting sphere with an excess charge. For any conductor in electrostatic equilibrium, the excess charge resides on the surface, and the electric field inside is zero. This phenomenon is a direct consequence of the properties of conductors and the application of Gauss's law.
Regarding a hollow conducting sphere with an excess charge of -10mC, the electric field inside this sphere would be 0 N/C. The charges distribute themselves on the outer surface of the conductor, and according to Gauss's law through a spherical surface inside the conductor, there would be no net enclosed charge, resulting in an electric field of zero.