An electromagnetic flowmeter is useful when it is desirable not to interrupt the system in which the fluid is flowing (e. g. for the blood in an artery during heart surgery). Such a device is illustrated. The conducting fluid moves with velocity v in a tube of diameter d perpendicular to which is a magnetic field B. A voltage V is induced between opposite sides of the tube. Given B = 0.120 T, d = 1.2 cm., and a measured voltage of 2.88 mV, determine the speed of the blood.

2 m/s

Explanation:

The electromagnetic flow-metre work on the principle of electromagnetic induction. The induced voltage is given as

where is the induced voltage = 2.88 mV = 2.88 x 10^-3 V

is the distance between the electrodes in this field which is equivalent to the diameter of the tube = 1.2 cm = 1.2 x 10^-2 m

is the velocity of the fluid through the field = ?

is the magnetic field = 0.120 T

substituting, we have

2.88 x 10^-3 = 0.120 x 1.2 x 10^-2 x

2.88 x 10^-3 = 1.44 x 10^-3 x

= 2.88/1.44 = 2 m/s

double the distance = divide strength by 4