A very small oil droplet of mass $6.9 \times 10^{-13}\,\text{kg}$ is stationary in an electric field of electric field strength $2.1 \times 10^{7}\,\text{N C}^{-1}$, as illustrated. The droplet’s weight is exactly counterbalanced by the electric force acting on it. Determine the charge on the droplet.
- A$3.3 \times 10^{-20}\,\text{C}$
- B$-3.3 \times 10^{-20}\,\text{C}$
- C$3.2 \times 10^{-19}\,\text{C}$
- D$-3.2 \times 10^{-19}\,\text{C}$