Question:
An air-filled parallel plate capacitor (d = 1mm, C = 20pF) is charged to 4.0µC. Find work done to increase plate separation to 5mm (constant charge).
An air-filled parallel plate capacitor (d = 1mm, C = 20pF) is charged to 4.0µC. Find work done to increase plate separation to 5mm (constant charge).
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Capacitance, energy, and work done
Updated On: Jan 13, 2026
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Solution and Explanation
U = Q²/2C. C = ε₀A/d. W = U_final - U_initial. C_initial = 20 pF. C_final = C_initial/5 = 4 pF. U_initial = 0.4 J. U_final = 2 J. W = 2 J - 0.4 J = 1.6 J.
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