The electric potential energy stored in the capacitor of a defibrillator is 64 J, and the capacitance is 137 µF. What is the potential difference that exists across the capacitor plates?

Answer 1

W = 0.5CV^2 = 64Joules,
0.5 * 137*10^-6 * V^2 = 64,
68.5*10^-6 * V^2 = 64,
V^2 = 64 / 68.5*10^-6 = 0.93*10^6,

V = sqrt(0.93*10^6) = 964.4 Volts.