A defibrillator is used to shock the heart of a patient by holding it to the pat

Question

A defibrillator is used to shock the heart of a patient by holding it to the patient's chest. The defibrillator contains a 32.7 F capacitor that, when fully charged, has a voltage of 3.00 kV across its parallel plates. How much stored energy is released into the patient's chest? When the defibrillator discharges across the patient's chest, the current through the patient first reaches a maximum of 30.0 A before fading to 0 A within a few milliseconds. What must be the resistance of the patient's chest?

Explanation / Answer

C = capacitance = 32.7 uF = 32.7 x 10-6 F

V = Voltage across the plates = 3000 Volts

Energy stored in patient's chest is given as

U = (0.5) CV2

U = (0.5) (32.7 x 10-6) (3000)2

U = 147.2 J

V = potential difference = 3000 Volts

R = resistance

i = maximum current = 30 A

using ohm's law

R = V/i = 3000/30 = 100 ohm

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