Step 1: Understanding the Concept:
An orifice is a small, well-defined opening in the side or bottom of a tank or in a plate placed in a pipeline, used for measuring or controlling fluid flow. For an orifice to function according to standard hydraulic formulas, its size must be small relative to the head of water and the size of the tank or pipe. The question asks for the typical range of the diameter of such an opening.
Step 2: Detailed Explanation:
1. Orifices are a fundamental device in fluid mechanics for flow measurement. They are classified based on size, shape, and the nature of the discharge.
2. A "small orifice" is one where the diameter of the opening is small compared to the head of the liquid above it (typically, diameter<H/5). This ensures that the velocity of flow through the opening can be considered uniform.
3. While there is no absolute standard that fits all applications, in the context of irrigation and hydraulic laboratory practice, the typical size for a standard circular orifice used for measurement is in a specific range.
4. The openings are large enough to avoid significant effects from surface tension and viscosity but small enough to be considered a true orifice rather than a sluice gate or other type of opening.
5. Let's review the options based on common practice:
1 to 2.5 cm: This is on the smaller side.
2.5 to 7.5 cm (approx. 1 to 3 inches): This range represents the most common sizes for standard orifices used in laboratory and small-scale field measurements. It's a practical size that balances the hydraulic assumptions with measurable flow rates.
8.0 to 9.5 cm and 10.0 to 11.5 cm: These are quite large and would be considered "large orifices" in many contexts, where the variation in head across the opening itself becomes significant and the simple orifice formula needs modification.
6. The given solution indicates option (B) is correct, which aligns with the common sizes used for standard hydraulic orifices.
Step 3: Final Answer:
The typical diameter of the opening in a standard orifice for flow measurement ranges from 2.5 to 7.5 cm. Therefore, option (B) is the correct answer.