Question 1 3AE02 - Third Assistant Engineer (Alt)

The Correct Answer is B ### Explanation for Option B (viscosity will increase) Viscosity is a measure of a fluid's resistance to flow. When high pressure is applied to hydraulic oil, the following occurs at the molecular level: 1. **Molecular Compression:** High pressure forces the oil molecules closer together, significantly increasing the density of the fluid. 2. **Increased Resistance:** This reduced spacing increases the intermolecular forces of attraction and the internal friction between the sliding layers of fluid. 3. **Result:** The fluid offers greater resistance to shear stress (flow), meaning the **absolute (dynamic) viscosity of the oil increases** when subjected to high operating pressure. This effect is measurable and often must be accounted for in precision hydraulic applications. *** ### Explanation of Incorrect Options **A) viscosity will decrease** Viscosity *decreases* primarily when the **temperature** of the oil increases. While temperature effects often dominate in hydraulic systems, the direct and immediate effect of applying pressure is always to increase viscosity. **C) volume will increase** Liquids, including hydraulic oil, are generally considered incompressible. When high pressure is applied, the oil molecules are forced closer together, causing the volume to **slightly decrease** (compression). The volume will never increase under pressure. **D) floc point will increase** The floc point is the temperature at which wax separates or precipitates out of the oil (most commonly discussed in relation to refrigeration systems). The floc point is a characteristic of the oil's chemical composition and is determined by temperature, not directly by the application of normal operating pressure in a hydraulic circuit.