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Energy stored in a capacitor

If the gap between the capacitor plates d {\displaystyle d} is constant, as in the parallel plate model above, the electric field between the plates will be uniform (neglecting fringing fields) and will have a constant value E = V / d {\displaystyle E=V/d}. In this case the stored energy can be calculated from the electric field strength W = 1 2 C V 2 = 1 2 ε A d (E d) 2 = 1 2 ε A d E 2 = 1 2 ε E 2 (volume of electric field) {\displaystyle W={\frac {1}{2}}CV^{2}={\frac {1}{2}}{\frac {\varepsilon A}{d}}\left(Ed\right)^{2}={\frac {1}{2}}\varepsilon AdE^{2}={\frac {1}{2}}\varepsilon E^{2}({\text{volume of electric field}})} The last formula above is equal to the energy density per unit volume in the electric field multiplied by the volume of field between the plates, confirming that the energy in the capacitor is stored in its electric field.