The drawing shows a type of flow meter that can be used to measure the speed of

Question

The drawing shows a type of flow meter that can be used to measure the speed of blood in situations when a blood vessel is sufficiently exposed (e.g., during surgery). Blood is conductive enough that it can be treated as a moving conductor .When it flows perpendicularly with respect to a magnetic field, as in the drawing, electrodes can be used to measure the small voltage that develops across the vessel. Suppose the speed of the blood is 0.32 m/s and the diameter of the vessel is 5.6 mm. In a 0.50-T magnetic field what is the magnitude of the voltage that is measured with the electrodes in the drawing? mV

Explanation / Answer

The force exerted by the electric field due to the electrodes will be equal to the magnetic force applied perpendicularly.

Fe = Fm

=> qE = qvBsin90o

=> E = qvB

also, Magnitude of Potential is related to Magnitude of Electric field by:

|V| = Ed

d is the separation between the plates.

therefore, |V| = vBd = 0.32 x 0.5 x 5.6 x 10-3 = 0.896 mV.

This is the voltage that will be measured by the electrodes.

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