Two parallel-connected planar capacitor charged from a source, then the source is turned off. Then, the distance between the plates of the first capacitor whose capacitance was 300 pF, reduced by half. As a result, the energy of the second capacitor (d2 = 4 mm, e = 2) was equal to 1.6 x 10 -7 J, and its bulk density of 8.85 × 10 -4 J / m ^ 3. Find the initial potential difference between the plates of the capacitor.

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