Question

With a neat diagram briefly describe the function of an open tube manometer.

Answer 1

Manometer: An open tube manometer is a tool used to measure a gas's pressure inside a container. As seen in the diagram, it is composed of a U-shaped tube filled with a liquid (let's assume mercury) with a density of ρ.

The tube has one end open to the atmosphere and one end attached to the vessel. The (unknown) pressure of the gas inside the vessel is represented by the pressure p at point A. The atmospheric pressure, or p₀, is the pressure on the mercury column in the open tube.

An open tube manometer

Point B is located at a depth of h from the mercury's surface in the open tube, at the same horizontal level as A. As a result, p₀ + ρgh represents the pressure at B. The unknown pressure p (at A) is equal to the pressure at B since the pressures at sites A and B at the same liquid level are equal.

p = 0 + ρgh

The difference between the pressures, p − p₀, is known as the gauge pressure, while the pressure p is known as the absolute pressure.