The defibrillator is essentially a capacitor whose electrodes are placed on the patient’s chest.
Capacity depends:
– the insulator between the armatures
– the strength and size of each armature, as well as the relative position between them.
Electric potential energy stored by a capacitor
In order to store energy in a capacitor, it is necessary to do work that is transformed into electrical potential energy . So, let’s consider the figure above, where we have an electrical circuit with a flat capacitor. If we close the circuit switch D , the capacitor will charge. In this way, its capacitance is given by , which results that the charge of the capacitor is, at each instant, directly proportional to its potential difference.
We can express this result through the Q x U graph shown below. The generator, by charging the capacitor, provided it with electrical potential energy. This energy stored by the capacitor is given, numerically, by the area A represented in the figure below.
E P = shaded area
In summary we have:
