Answer to Question #237978 in Electricity and Magnetism for Arvin Shopon

Question

There are ions in the blood, so the blood vessel can be modeled as a guide. Blood flow rate can be measured by placing a blood vessel in a magnetic field. In this case, the blood can be modeled as a conductor moving in a magnetic field to which a source voltage is induced according to the right-hand rule.

a) Blood flows at velocity v . Which one in the picture, A or B, is the positive pole of the voltmeter?

b) The vessel is 1.8 mm thick and is placed in a magnetic field with a magnetic flux density of 89 mT. The voltmeter shows 0.11 mV. Based on this, how high is the blood flow rate?

Answer 1

a) Depends on the picture, but the direction can be found with right-hand rule:

1. Place your palm with 4 fingers looking along the direction of motion of positive ions

2. Orient it so the magnetic field lines come to the inner side of your palm

3. The thumb at 90° to the four fingers would show the direction where the positive voltage is generated.

b) As we know:

$$E=BLv,\\\space\\ v=\frac{E}{BL}=0.69\text{ m/s}.$$