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Defibrillators (redirected from Defibrilators)

Page history last edited by Ben Dreyfus 5 years, 6 months ago

8.5.P22

 

The electrical signals to the heart are typically coordinated to create a wave of compression that travels across the heart to pump the blood through the heart chambers. If these signals get misaligned, the bits of the heart muscle vibrate independently and as a result do not move blood. This situation is called fibrillation and can quickly lead to death.

 

If the situation is caught in time, passing a jolt of current through the heart can realign the electrical signals in the heart and start it beating again. The device that delivers this current is a defibrillator. (See the figure at the right.) The heart of a heart defibrillator is a big capacitor. A battery takes perhaps half a minute to charge this capacitor. This capacitor has a capacitance of 54 μF (microFarads) and, when turned on, is charged by a battery to 4,200 Volts.

A. How much charge (Q) is stored on each plate of the capacitor when it is fully charged and how much energy does it store?

B. The energy in the capacitor is delivered by placing paddles on either side of the victim’s heart as shown in the figure at the right.

 

The defibrillator delivers that charge in a millisecond through the paddles, and the hope is that the shock resets the heart so it can begin beating normally. The charge is delivered in a sudden pulse that lasts about 100 ms. What is the average current, I, flowing through the body?

C. If all the energy stored in the capacitor is delivered in electric current, what is the voltage difference at which the current was delivered?

 

D. Calculate the effective resistance, R, of the path of the current through the body.

 

 

Joe Redish 5/2/13

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