Question

At a distance of 0.75 meters from its center, a Van der Graff generator interacts as if it were a point charge, with that charge concentrated at its center. A test charge at that distance experiences an electric field of 4.5 × 105 newtons/coulomb. What is the magnitude of charge on this Van der Graff generator?
a.1.7 × 10-7 coulombs
b.2.8 × 10-7 coulombs
c.3.0 × 10-7 coulombs
d.8.5 × 10-7 coulombs