A flat square sheet of charge (side 50 cm) carries a uniform surface charge density. An electron 0.5 cm from a point near the center of the sheet experiences a force of 1.8×10−12N directed away from the sheet. Determine the total charge on the sheet
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Solution
Electron is 0.5 cm from the sheet of charge and is far away from the edges of the sheet. Therefore, the sheet looks effectively infinite.
E=σ2ε0=q2ε0A or F=−eE=−e(q2ε0A) q=−2ε0AFe =−2(8.854×10−12)×(0.5)2×(1.8×10−12)1.6×10−19 =−50μC