86. For Bingham Plastics and pseudo plastic liquids, the apparent viscosity:
A. Increases with increase in shear force
B. Decreases with increase in shear force
C. Remains constant with increase in shear force
D. Changes in an unpredictable fashion with change in shear force

Detailed Explanation:

In fluid mechanics and rheology, understanding how fluids behave under shear is crucial. Two common types of non-Newtonian fluids—Bingham plastics and pseudoplastic liquids—demonstrate shear-dependent viscosity, unlike Newtonian fluids, whose viscosity remains constant regardless of the applied shear.

What Are Bingham Plastics?

Bingham plastics behave as a rigid body at low stresses, but once a yield stress is exceeded, they flow like a viscous fluid. Examples include toothpaste and mayonnaise.

• Before yield stress: No flow occurs.

• After yield stress: The fluid begins to flow, and the apparent viscosity decreases as shear force increases.

What Are Pseudoplastic Liquids?

Pseudoplastic fluids, also known as shear-thinning fluids, become less viscous with increased shear rate. Common examples include ketchup, paint, and blood.

• As shear increases, the internal resistance to flow decreases.

• This makes them ideal in processes requiring easy spreading or pumping.

Apparent Viscosity:

In both types of fluids:

• Apparent viscosity is defined as the ratio of shear stress to shear rate.

• It decreases as shear force increases, meaning they become easier to flow under higher stress.

Correct Answer:

B. Decreases with increase in shear force