WAEC Physics 2020 Paper

Concept:Viscosity is the internal friction that opposes the relative motion between fluid layers, and it is a property of the fluid itself.Explanation:Viscosity occurs in both liquids and gases because adjacent layers exert tangential frictional forces on each other during flow.The coefficient of viscosity, $\eta$, is a fluid property that is independent of the area of the surfaces in contact and independent of the relative velocity of the layers for ordinary fluids.The viscous force, however, does depend on area and velocity gradient: $F = \eta A \frac{dv}{dy}$.Thus, confusing viscosity with viscous force makes option A false.Since viscosity occurs in fluids, option B is true.Since $\eta$ is not affected by relative velocity of layers, option C is true.The tangential force between layers is related to viscous friction, so option D does not contradict the correct idea.Therefore, the untrue statement is option A.Answer:A. depends on areas of the surfaces in contact