A small, spherical dust grain in a vacuum chamber has an electric field strength of 4.5 × 104 V m-1 at a distance of 1.2 mm from its center. What is the net charge on the dust grain?
1.8×10−12 C1.8 \times 10^{-12}\text{ C}1.8×10−12 C
6.0×10−9 C6.0 \times 10^{-9}\text{ C}6.0×10−9 C
7.2×10−12 C7.2 \times 10^{-12}\text{ C}7.2×10−12 C
7.2×10−6 C7.2 \times 10^{-6}\text{ C}7.2×10−6 C
