A heart surgeon can monitor the blood flow rate through an artery using an elect

Question

A heart surgeon can monitor the blood flow rate through an artery using an electromagnetic flowmeter. (See Figure 5). Electrodes A and B make contact with the outer walls of the blood vessel, which has a diameter of 1.8 mm. When a magnetic field of 0.027 T is applied by the poles of the magnet, an emf of 126 mu V appears between the electrodes. Calculate the speed of the blood flowing in the vessel. In the diagram, electrode A is shown as positive, and electrode B is negative. Does this have to be the case, or could electrode A be negative? (In other words, does the sign of the emf depend on whether the charge carriers in the blood are predominantly positively or negatively charged?)

Explanation / Answer

a)We know that in the magnetic flowmeter

E= B d V

where d is the diameter of the vessel, V the velocity of blood

126 E-6 = .027 *.0018 * V

V = 126/27*1.8= 2.6 m/s

No the direction doesn't change the effect as the velocity is dependent on magnitude.

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