Officer Aptitude Rating (OAR) Complete Practice Test 2025

Increasing the diameter of a pipe typically leads to a reduction in flow speed. As the diameter increases, the cross-sectional area of the pipe also increases, allowing more fluid to flow through. According to the principle of continuity in fluid dynamics, if the flow rate (the amount of fluid passing through a section per unit time) remains constant, an increase in cross-sectional area results in a decrease in flow speed. This is because the same volume of fluid now has more space to occupy, so it moves slower.

In practical terms, in a wider pipe, the fluid has a greater area to spread out, which naturally slows its velocity compared to that in a narrower pipe. It's important to note that while the flow speed decreases, the overall volume of fluid that can flow per unit time may increase, provided the pressure driving the fluid remains the same.

The other choices do not align with the principles of fluid flow. Increasing flow resistance typically occurs with a decrease in diameter or with obstructions, while having no effect on flow speed contradicts the foundational concepts of fluid dynamics. As such, the assertion that increasing the diameter leads to reduced flow speed accurately reflects the behavior of fluids in varying pipe diameters.