Question

A heart defibrillator is used to enable the heart to start beating if it has stopped. This is done by passing a large current of 12 A through the body at 29 V for a very short time, usually about 3.3 ms .

A.) What power does the defibrillator deliver to the body? ________ W

B.) How much energy is transferred? _______ J

Answer 1

Electric power is defined as P=IV, where I is current and V is voltage.

In this problem, I = 12.0 A and V = 29.0V so

P = IV = 12.0 A * 29.0 V = 348 W

The energy transfered depends on the time according to the definition of power as P = E/t where t is the amount of time over which the energy is transfered.

In this problem, t = 3.3 ms = 0.0033 s (to cancel the units properly) and P = 348 W from the first half, so

348 W = E / 0.0033 s, solve for E by multiplying both sides by 0.0033 s yields

E = 348 W * 0.0033 s = 1.1484 J