Which type of meter has no moving parts?

The correct choice is the type of meter that has no moving parts, which is a magnetic meter. Magnetic meters operate by measuring the velocity of a fluid as it flows through a magnetic field. This is accomplished using Faraday's law of electromagnetic induction, which states that a voltage is produced when a conductive fluid passes through a magnetic field. Since the fluid flow generates this voltage without any mechanical movement inside the meter, it does not have moving parts.

This design allows for a number of advantages, such as reduced wear and tear, lower maintenance requirements, and the ability to measure a wide range of flow rates accurately and reliably. They are especially useful in applications involving dirty or corrosive fluids where other types of meters might have issues.

In contrast, propeller meters have moving parts because they rely on a spinning propeller to measure flow, while rotameters use a float that rises and falls in a tapered tube, indicating flow based on its position. Venturimeters also contain components that cause the flow to divert and create pressure differences, measuring flow based on these changes, which means they also include moving parts. Thus, magnetic meters stand out for their simple, efficient design that eliminates mechanical components, emphasizing their reliability and accuracy for measuring fluid flow.