# A heart defibrillator being used on a patient has an RC time constant of 14.0 ms.?

(a) If the defibrillator has a 7.40 µF capacitance, what is the resistance (in kΩ) of the path through the patient? (You may neglect the capacitance of the patient and the resistance of the defibrillator.)

(b) If the initial voltage is 12.0 kV, how long (in ms) does it take to decline to 5.20 ✕ 10^2 V?

### 1 Answer

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- Andrew SmithLv 71 year agoFavorite Answer
7.40 * 10 ^ -6 * R = 14.0 * 10 ^ -3

now what is the question here?

R= 1.89 * 10 ^ 3 ohm

b) V = Vo e^ ( -t / RC)

V/Vo = e^(-t / RC)

take the natural log of both sides

ln(V/Vo) = - t / RC

t = - RC * ln( V/Vo)

= - 14* 10^-3 * ln(5.20 * 10 ^ 2 / ( 12 * 10 ^ 3) )

~= 0.044 s [But YOU check the arithmetic. and the working too. ]

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