Orifices and Mouthpieces MCQ with answer and solution

Concept

A mouthpiece is a short tube fitted to an orifice. The coefficient of discharge of an external mouthpiece depends primarily on its length relative to its diameter.

Step-by-step solution

1. Understand what an external mouthpiece is. It is a short pipe fitted to an opening in the tank. 2. The flow characteristics depend on the dimensions of this short pipe, especially its length and diameter. 3. Hydraulics theory shows that the coefficient of discharge for a standard external mouthpiece depends on the length of the mouthpiece. Answer: (D) Length of mouthpiece

Explanation

For an external cylindrical mouthpiece, the coefficient of discharge depends mainly on the length of the mouthpiece relative to its cross-sectional dimensions. A standard running length is about two to three times the diameter.

Why the other options are wrong

A: Velocity affects flow rate, not the discharge coefficient itself. B: Pressure head determines velocity, not the discharge coefficient. C: Area is part of the overall flow calculation, but the coefficient itself depends on the geometric proportions, particularly length.

Shortcut

Remember that external mouthpieces are classified by length, which directly affects the jet contraction and coefficient of discharge.

Common mistake

Thinking that velocity or pressure of the liquid directly changes the coefficient of discharge, which is a dimensionless ratio.