What principle does a magnetic flowmeter use to measure flow in a conductive liquid?

What principle does a magnetic flowmeter use to measure flow in a conductive liquid?

• A. Faraday’s law of induction; a magnetic field induces a voltage in the moving conductive liquid, which is sensed by electrodes.
• B. Bernoulli principle explains pressure differences in pipe flow.
• C. Archimedes' principle governs buoyant forces in fluids.
• D. Ohm’s law relates voltage, current, and resistance in a conductor.

Answer: (A)

Magnetic flowmeters operate on Faraday’s law of induction. When a conductive liquid moves through a magnetic field, it experiences an electromotive force that is proportional to its velocity. In a mag meter, coils create a magnetic field across the pipe, and as the liquid flows, charges in the liquid are moved by the Lorentz force, generating a voltage between two electrodes on the pipe wall. That induced voltage is measured and is directly related to the flow velocity; by knowing the pipe cross-sectional area, the instrument computes the volumetric flow rate. The method works regardless of pressure or density changes, as long as the liquid conducts electricity. The other ideas don’t describe how a magnetic flowmeter measures flow: Bernoulli’s principle explains pressure differences due to velocity changes but isn’t used to sense flow in this type of meter; Archimedes’ principle relates to buoyant forces and isn’t involved; Ohm’s law describes a conductor’s V = IR relationship, not the flow-induced voltage generated by motion in a magnetic field.

Magnetic flowmeters operate on Faraday’s law of induction. When a conductive liquid moves through a magnetic field, it experiences an electromotive force that is proportional to its velocity. In a mag meter, coils create a magnetic field across the pipe, and as the liquid flows, charges in the liquid are moved by the Lorentz force, generating a voltage between two electrodes on the pipe wall. That induced voltage is measured and is directly related to the flow velocity; by knowing the pipe cross-sectional area, the instrument computes the volumetric flow rate. The method works regardless of pressure or density changes, as long as the liquid conducts electricity.

The other ideas don’t describe how a magnetic flowmeter measures flow: Bernoulli’s principle explains pressure differences due to velocity changes but isn’t used to sense flow in this type of meter; Archimedes’ principle relates to buoyant forces and isn’t involved; Ohm’s law describes a conductor’s V = IR relationship, not the flow-induced voltage generated by motion in a magnetic field.