C₁ = ε₀·Ad₁ = 8.85·10⁻¹² · 10⁻²2·10⁻³ = 44.25 pF
Q = C₁·V = 44.25·10⁻¹² · 12 = 5.31·10⁻¹⁰ C
U₁ = Q²2·C₁ = 3.19·10⁻⁹ J C₂ = 22.125 pF U₂ = Q²2·C₂ = 6.37·10⁻⁹ J
W_ext = ΔU = U₂ − U₁ = 3.19·10⁻⁹ J ≈ 3.19 nJ
F = Q²2·ε₀·A = (5.31·10⁻¹⁰)²2 · 8.85·10⁻¹² · 10⁻² = 1.59·10⁻⁶ N
W_ext = F·Δd = 1.59·10⁻⁶ · 2·10⁻³ = 3.19·10⁻⁹ J ✓
W_ext = ½·V²·(C₁ − C₂) = 0.5 · 12² · 22.125·10⁻¹² = 1.59·10⁻⁹ J ≈ 1.59 nJ
ΔU = −1.59 nJ V·ΔQ = −3.19 nJ W_ext = ΔU − V·ΔQ = 1.59 nJ ✓