A student adjusts the capacitance of an isolated parallel-plate capacitor with a charge of 500 μC from 8.5 μF to 3.5 μF by modifying the distance between the plates using an external force. Find the work done by the external force during this adjustment.

• A. 2.1 × 10^-2 J
• B. 5.6 × 10^-2 J
• C. 2.1 J
• D. 5.6 J

Answer: (A)