Final answer:
The rate of flow of a liquid through a metering orifice or jet will be the greatest when the cross-sectional area of the orifice or jet is the smallest. The equation of continuity states that as the cross-sectional area decreases, the speed of the fluid increases. This is why the fluid flows fastest through a narrow spray nozzle.
Step-by-step explanation:
The rate of flow of a liquid through a metering orifice or jet will be the greatest when the cross-sectional area of the orifice or jet is the smallest. According to the equation of continuity, when the cross-sectional area decreases, the speed of the fluid increases. This means that the flow rate will be highest when the orifice or jet has the smallest diameter. For example, water flowing through a narrow spray nozzle will emerge with a large speed, while it will slow down when it enters a larger-diameter region.