A thin circular sheet of glass of diameter 7 meters is rubbed with a cloth on one surface, and becomes charged uniformly. A chloride ion (a chlorine atom which has gained one extra electron) passes near the glass sheet. When the chloride ion is near the center of the sheet, at a location 0.7 mm from the sheet, it experiences an electric force of 7e-15 N, toward the glass sheet. In this problem, use the value ?0 = 8.85e-12 C^2/(N)