Just as every circuit has a small amount of extra resistance in the wires, which we usually neglect, every circuit also has a small amount of stray capacitance and self-inductance because of the geometry of the wires. Consider a pacemaker implant in which the leads travel close together from the device to the heart, then separate and connect to the top and bottom of the heart. The circuit completes through the middle of the heart, so take the area of the current loop to be half the cross‑sectional area of the heart. The current loop is approximately a circle of radius 4. 0 cm. Approximate the magnetic field as constant inside the loop and equal to the value at the center of the loop. Use this field to get the magnetic flux through the loop and hence estimate the stray self-inductance l of the loop.