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$\mathbf{12}\mathbf{A}$through the body at$\mathbf{25}\mathbf{}\mathbf{V}$for a very short time, usually$\mathbf{3}\mathbf{.}\mathbf{0}\mathbf{}\mathbf{ms}$about . (a) What power does the defibrillator deliver to the body, and (b) how much energy is transferred ?

Short answer

1. The power delivered by the defibrillator to the body is$300\mathrm{V}$.
2. The energy transferred to the body is$0.90\mathrm{J}$.

Step-by-step solution

Concept/Significance of maximum power transfer.

As the load resistance is equal to the network's resistance when seen from output terminals with all energy sources removed and only the network's internal resistance remaining, maximum power transfer occurs.

(a) Determination of power delivered by the defibrillator to the body

Power delivered by the voltage source is given by,

$P=IV$

Here,I is the current passed through the body and V is the potential at which current is passed.

Substitute all the values in the above,

$$\begin{gathered} P=\left(12A\right)\left(25V\right) \\ =300V \end{gathered}$$

Thus, the power deliver by the defibrillator to the body is$300V$.

(b) Determination of the energy transferred to the body

The energy transferred is given by,

$E=Pt$

Here, P is the power delivered by the defibrillator and t is the time taken.

Substitute all the values in the above,

$$\begin{gathered} E=\left(300W\right)\left(3\times {10}^{-3}S\right) \\ =0.90\mathrm{J} \end{gathered}$$

Thus, the energy transferred to the body is$0.90\mathrm{J}$.