For a 'submerged orifice', the discharge Q is calculated using:
Choose the correct answer
Q = Cd×A×√(2g×H1) using upstream head only
Q = Cd×A×√(2g×(H1−H2)) — differential head between upstream and downstream drives flow
Q = Cd×A×H1² (squared head)
Q = Cd×A×(H1+H2)/2
Correct Answer
B. Q = Cd×A×√(2g×(H1−H2)) — differential head between upstream and downstream drives flow
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Submerged orifice (tailwater above orifice): Q = Cd × A × √(2g × (H1−H2)) where H1 = upstream water depth above orifice centre, H2 = downstream depth above orifice centre, (H1−H2) = differential head. Cd ≈ 0.61 (same as free orifice). Key: only differential head drives flow — not H1 alone. Contrast: free orifice (tailwater below): Q = Cd×A×√(2gH1).
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