Physics II / Electrostatic Energy and Forces
Practice question · Numerical answer

A capacitor of 2.0 μF is charged to 100 V. Compute the stored energy in mJ.

Hints
  1. Use one half C V squared.
  2. Compute 0.5 x 2.0e-6 x 100^2.
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10 (answers within ±0.2 count)

Why

U=12CV2=0.5×2.0×10−6×104=10−2U = \tfrac{1}{2}CV^2 = 0.5 \times 2.0 \times 10^{-6} \times 10^4 = 10^{-2} J =10= 10 mJ. The quadratic dependence on voltage is why capacitor ratings matter so much.

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