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Chapter 19 | Electric Potential and Electric Field 865
Figure 19.31 Automated external defibrillators are found in many public places. These portable units provide verbal instructions for use in the important first few minutes for a person suffering a cardiac attack. (credit: Owain Davies, Wikimedia Commons)
Example 19.11 Capacitance in a Heart Defibrillator
A heart defibrillator delivers of energy by discharging a capacitor initially at . What is its capacitance?
Strategy
We are given and , and we are asked to find the capacitance . Of the three expressions in the equation for
, the most convenient relationship is Solution
(19.77)
(19.78)
Solving this expression for and entering the given values yields
Discussion
This is a fairly large, but manageable, capacitance at .
Glossary
capacitance: amount of charge stored per unit volt
capacitor: a device that stores electric charge
defibrillator: a machine used to provide an electrical shock to a heart attack victim's heart in order to restore the heart's normal rhythmic pattern
dielectric: an insulating material
dielectric strength: the maximum electric field above which an insulating material begins to break down and conduct electric potential: potential energy per unit charge
electron volt: the energy given to a fundamental charge accelerated through a potential difference of one volt
