Which of the following statements is/are true? i. Dynamic viscosity is the resistance to movement of one layer of a fluid over another. ii. The unit of dynamic viscosity is Pascal-second. iii. Kinematic viscosity is expressed as the ratio of fluid dynamic viscosity to its density. iv. The unit of measurement of kinematic viscosity is m²s⁻¹.
- AOnly (i) and (ii)
- BOnly (iii) and (iv)
- COnly (i) and (iii)
- D(i), (ii), (iii) and (iv)Correct
Solution
Concept
Properties and units of fluid viscosity
Formula
NONE
Step-by-step solution
1. Dynamic viscosity measures internal fluid friction between adjacent layers, with SI units of Pascal-second (Pa·s). 2. Kinematic viscosity is dynamic viscosity divided by fluid density, measured in m²s⁻¹ in SI units. 3. Statements i, ii, iii, and iv are all correct statements of fluid mechanics principles. Answer: D
Explanation
Dynamic viscosity measures fluid resistance to shear, expressed in Pascal-seconds, while kinematic viscosity is the ratio of dynamic viscosity to density, measured in m²s⁻¹. Because all four statements accurately state basic fluid mechanics definitions and units, option D is correct.
Why the other options are wrong
A) Statements (iii) and (iv) are also correct regarding kinematic viscosity definitions and units. B) Statements (i) and (ii) are also true regarding dynamic viscosity properties and units. C) Statements (ii) and (iv) are also valid statements about viscosity units and concepts.
Shortcut
All four statements are correct: dynamic viscosity is Pa·s and kinematic viscosity is m²/s.
Common mistake
Selecting option A or C by incorrectly assuming the units or formula for kinematic viscosity are incorrect.
Correct answer: D) (i), (ii), (iii) and (iv)