What does a Rotameter consist of?

A Rotameter is a type of flowmeter used to measure the flow rate of liquids and gases in a closed tube. Its fundamental design features a tapered metering tube and a float that moves up and down within this tube. The float is typically plug-shaped, allowing it to rise higher as the flow rate increases, which alters the cross-sectional area available for the fluid to pass.

In this device, as the flow rate increases, the fluid lifts the float to a point where the upward force of the flow balances the weight of the float. The position of the float within the tapered tube directly correlates to the flow rate, making it easy to read the flow directly against a scale usually printed on the tube's side. The plug-like shape of the float ensures stability and effective measurement across a range of flow conditions, which is why this option correctly describes a Rotameter.

Other choices, while related to different instruments or measurement techniques, do not accurately reflect the components or functionality of a Rotameter, making them unsuitable for this question.