Consider the following statements regarding sedimentation analysis of soil particles based on Stokes’ law : 1. The finer soil particles are never perfectly spherical. 2. All the soil grains may have the same specific gravity. 3. Particles constituting to fine soil fraction may carry surface electric charges. Which of the above statements are correct ?
- A1 and 2 only
- B1 and 3 only
- C2 and 3 only
- D1, 2 and 3Correct
Solution
Concept
Assumptions and limitations of sedimentation analysis
Step-by-step solution
1. Stokes' law assumes spherical particles, but fine particles are flaky (a limitation) (1 true). 2. It assumes that all grains have the same specific gravity, which may not hold (2 as an assumption true). 3. Fine particles carry electric charges, so a dispersing agent is needed (3 true).
Explanation
The three statements are standard comments on the assumptions and limitations of Stokes' law in hydrometer analysis.
Why the other options are wrong
Each of the other options omits one of the statements.
Shortcut
Stokes: spherical, same G, dispersed particles.
Common mistake
Leaving out one statement.
Correct answer: D) 1, 2 and 3