Orifice meter is used to measure:

Concept:

orifice meter:

• An orifice meter is a device with a hole in it, which measures how fast a fluid is flowing, by recording the pressure decrease across the hole. The two most important factors that influence the reading of an orifice meter are the size of the orifice and the diameter of the pipe which it is fitted into.
• It is used to measure the flow rate of a gas or a fluid.
• It mainly consists of an orifice plate, an orifice plate housing, and a meter tube.

Explanation:

Discharge of orifice meter

\({\bf{Q}} = {{\bf{C}}_{\bf{d}}} \times \frac{{{{\bf{A}}_1}{{\bf{A}}_{\bf{o}}}\sqrt {2{\bf{gh}}} }}{{\sqrt {{\bf{A}}_1^2 - {\bf{A}}_{\bf{o}}^2} }}\)

Where Cd = coefficient of discharge = 0.64 to 0.76

A1 = Area of vena contracta

Ao = Area of orifice 

h = Difference in heads.

Mistake PointsThe coefficient of discharge for the orifice meter varies between 0.64 - 0.65, but here none of the options are perfectly correct so we have to mark the most appropriate options.