Measuring Blood Flow. Blood contains positive and negative ions and thus is a conductor. A blood vessel, therefore, can be viewed as an electrical wire. We can even picture the flowing blood as a series of parallel conducting slabs whose thickness is the diameter 5.28 of the vessel moving with speed. If you expect that the blood will be flowing at 14.8 cm / s for a vessel4.80 mm in diameter, what strengthof magnetic field will you need to produce a potential differenceof 1.00 mV?