Q1: An orifice is taken as large if

ANS:D - (H₂ - H₁) > H/3

The condition (H2−H1)>H/3​ indicates that the difference in the upstream and downstream heads (H2−H1) is greater than one-third of the height of the liquid above the orifice (denoted by H). This condition suggests that for an orifice to be considered large, the difference in the heads must be substantial compared to the height of the liquid column above the orifice. If the difference in heads is more than one-third of the height of the liquid column, it suggests that the orifice size is significant relative to the height of the liquid column. Practically, a large orifice implies that the orifice size is substantial enough compared to the height of the liquid column, such that it significantly affects the flow behavior and discharge characteristics. In engineering applications, the distinction between large and small orifices is important for accurately predicting flow rates, pressure drops, and other flow parameters. Large orifices often exhibit different flow characteristics compared to small orifices, and engineers consider these distinctions when designing and analyzing fluid systems. Therefore, when (H2−H1)>H/3​, it suggests that the orifice is relatively large compared to the height of the liquid column above it.