One device in which capacitors have an important role is the defibrillator (Fig. 26.14).
Up to 360 J is stored in the electric field of a large capacitor in a defibrillator when it is
fully charged. The defibrillator can deliver all this energy to a patient in about 2 ms. (This
is roughly equivalent to 3 000 times the power delivered to a 60-W lightbulb!) Under the
proper conditions, the defibrillator can be used to stop cardiac fibrillation (random contractions)
in heart attack victims. When fibrillation occurs, the heart produces a rapid,
irregular pattern of beats. A fast discharge of energy through the heart can return the
organ to its normal beat pattern. Emergency medical teams use portable defibrillators
that contain batteries capable of charging a capacitor to a high voltage. (The circuitry
actually permits the capacitor to be charged to a much higher voltage than that of the
battery.) The stored energy is released through the heart by conducting electrodes, called
paddles, that are placed on both sides of the victim’s chest. The paramedics must wait between
applications of the energy due to the time necessary for the capacitors to become
fully charged. In this case and others (e.g., camera flash units and lasers used for fusion
experiments), capacitors serve as energy reservoirs which can be slowly charged and then
discharged quickly to provide large amounts of energy in a short pulse.