In a magnetic flowmeter, water passing through the magnetic field induces a small flow of electrified current that is _______, which is converted to flow rate.

• A. proportional to density
• B. proportional to velocity
• C. proportional to pressure
• D. proportional to velocity

Answer: (D)

In a magnetic flowmeter, the moving conductive water in a magnetic field generates an electric signal by Faraday’s law that is proportional to how fast the water is moving. That induced voltage (or current) is determined by the fluid velocity, not by density or pressure. The meter then converts that velocity signal into a volumetric flow rate by taking into account the pipe’s cross-sectional area (flow rate = velocity × area). So the best description is that the induced current is proportional to velocity, which is then translated into flow rate. The signal doesn’t directly depend on density or pressure.