Terminology — Short Pipe Fitted to an Orifice A pipe whose length is greater than about twice the orifice diameter, fitted externally or internally to the orifice, is termed as:

Introduction:
Distinguishing between notches, weirs, orifices, mouthpieces, and nozzles is foundational. Each device has a characteristic geometry and flow regime leading to different discharge equations and coefficients.

Given Data / Assumptions:

• Short pipe attached to an orifice.
• Length exceeds roughly 2 times the orifice diameter.
• Liquid discharge under hydrostatic head.

Concept / Approach:
Mouthpieces are short tubes that modify the jet formation and reduce contraction relative to a thin-plate orifice. This changes coefficients (Cc, Cv, Cd) and energy losses. Notches/weirs are open-channel overflow structures; a nozzle is a shaped duct usually to convert pressure to velocity efficiently but is much longer and shaped than a simple short tube.

Step-by-Step Solution:
Check definition: short tube L ≳ 2d attached to an orifice = mouthpiece.Other terms do not match the described geometry.Therefore, select ‘‘mouthpiece’’.

Verification / Alternative check:
Textbook definitions consistently identify the L/d criterion to distinguish a mouthpiece from a mere orifice opening.

Why Other Options Are Wrong:
Notch/weir are overflow devices; nozzle implies a longer, shaped passage; they are not simply short pipes at orifices.

Common Pitfalls:
Calling any short attachment a nozzle; forgetting that mouthpieces may be internal or external and may run free or full.

Final Answer:
mouthpiece