General characteristics of water wheels Which of the following statements about traditional water wheels is/are correct?

Introduction / Context:
Before modern turbines, water wheels (overshot, breastshot, undershot) were widely used to convert hydraulic energy into mechanical work. Understanding their operating traits clarifies why turbines replaced them in many applications and where water wheels still make sense (e.g., heritage mills, micro-hydro with very low heads).

Given Data / Assumptions:

• Low to moderate heads and variable streams.
• Simple construction with buckets/paddles; open-channel approach flow.
• Speed governed by wheel diameter and flow; no high-speed gearing assumed.

Concept / Approach:
Water wheels rely on weight (overshot), impulse (undershot), or a combination (breastshot). Their large diameters and direct mechanical linkage lead to low rotational speeds. Overshot/breastshot types can use small heads effectively. Because of their broad buckets and inertia, efficiency can remain reasonably steady across moderate discharge changes, though not as high or as flat as modern turbines.

Step-by-Step Solution:
Low head suitability: overshot/breastshot can operate on a few meters or less.Slow speeds: large wheels with direct drive rotate slowly compared to turbines.Efficiency variation: within typical operating ranges, efficiency is fairly stable though absolute peak is lower than Francis/Kaplan.

Verification / Alternative check:
Historical performance records and modern reconstructions show efficiencies in the 60–80% range depending on type, relatively constant over moderate flow fluctuations.

Why Other Options Are Wrong:
Each of (a), (b), and (c) is broadly correct in context; “none of the above” is therefore wrong.

Common Pitfalls:
Comparing water wheels directly to high-specific-speed turbines; ignoring that severe flow variations still reduce efficiency.

Final Answer:
all of the above