Question

HOW many excess electrons must be added to an isolated spherical conductor 0.100 meters in diameter to produce an electric field of 1800N/C just outside the surface?

Answer 1

The field is

$$E=\frac{Q}{4\pi \epsilon_0r^2}=\frac{Ne}{4\pi \epsilon_0r^2},\\\space\\ N=\frac{4\pi \epsilon_0r^2E}{e}=1.25·10^{10}.$$