**A heart pacemaker consists of a switch, a battery of constant voltage E _{0} , a capacitor with constant capacitance C, and the heart as a resistor with constant resistance R. When the switch is closed, the capacitor charges; when the switch is open, the capacitor discharges, sending an electrical stimulus to the heart.During the time the heart is being stimulated, the voltage E across the heart satisfies the linear differential equation**

Solve the DE, subject to E(4) =E _{0} .

I’ll start attacking this problem by observing that the given differential equation is separable. So i’ll do the separation as follows:

.

I’ll then integrate both sides of the equation as follows:

On integration we get:

Here , k is a constant of integration. I’ll then make E(t) the subject of the formula by introducing an exponential on both sides, so that:

The exponential on the right side of the equation can be broken down into two terms using the laws of indices as follows:

But e^{k} is just a constant. Therefore ,we can rewrite the above equation as follows:

Here,

The expression for E(t) then becomes;

We are given the following boundary condition: E(4) =E _{0}. Plugging this into E(t),

Solving for A we get:

Therefore E(t) becomes:

Merging the two exponential terms ,we get the following:

That is the solution for E(t) in terms of the given constants and time t. The negative sign on the exponential term indicates a ‘decay’ in the voltage when the capacitor is discharging.