Flow properties of powders are vital in pharmaceutical formulation and processing, influencing blending, granulation, tablet compression, capsule filling and inhalation delivery. B. Pharm students must understand how particle size, shape, surface texture, moisture, cohesion, density and size distribution govern powder flow. Key measurements include angle of repose, bulk and tapped density, Carr’s index, Hausner ratio, shear cell testing and powder rheometry, while common tools include funnel tests, tapped density testers and shear testers. Interpreting these results helps troubleshoot caking, segregation, hopper design and scale-up. This concise overview emphasizes practical interpretation and control of powder flow in drug manufacturing. Now let’s test your knowledge with 30 MCQs on this topic.
Q1. What does the angle of repose primarily measure for a pharmaceutical powder?
- The maximum shear stress of a powder under compression
- The static friction between powder and metal surfaces
- The steepest angle at which a powder heap remains stable
- The porosity of a compacted powder bed
Correct Answer: The steepest angle at which a powder heap remains stable
Q2. Which range of angle of repose typically indicates good flowability?
- Less than 30°
- 30°–40°
- 40°–50°
- Greater than 50°
Correct Answer: Less than 30°
Q3. How is Carr’s compressibility index (CI) calculated?
- CI = (Bulk density − Tapped density) × 100
- CI = (Tapped density − Bulk density) / Tapped density × 100
- CI = Tapped density / Bulk density
- CI = Angle of repose × 100
Correct Answer: CI = (Tapped density − Bulk density) / Tapped density × 100
Q4. The Hausner ratio is defined as:
- Bulk density divided by tapped density
- Tapped density divided by bulk density
- Tapped density minus bulk density
- Inverse of Carr’s index
Correct Answer: Tapped density divided by bulk density
Q5. Typical interpretation: a Hausner ratio less than which value suggests good flow?
- 0.75
- 1.05
- 1.25
- 1.75
Correct Answer: 1.25
Q6. Which instrument is commonly used to determine bulk and tapped densities?
- Angle of repose apparatus
- Tapped density tester
- Ring shear tester
- Spray dryer
Correct Answer: Tapped density tester
Q7. Which factor generally increases powder cohesion and reduces flowability?
- Large, spherical particles
- Low surface moisture
- High electrostatic charges and fine particles
- Wide particle size distribution
Correct Answer: High electrostatic charges and fine particles
Q8. In shear cell testing, the unconfined yield strength (σc) is used to calculate:
- Bulk density
- Flow function or flowability index (ffc)
- Hausner ratio
- Angle of repose
Correct Answer: Flow function or flowability index (ffc)
Q9. Which of the following powder changes typically improves flow for tableting?
- Increasing fines and humidity
- Granulation to produce larger, more spherical particles
- Reducing particle size to submicron range
- Increasing surface roughness
Correct Answer: Granulation to produce larger, more spherical particles
Q10. Carr’s index value above which is generally considered to indicate poor flow?
- Less than 10%
- 10%–15%
- 20%–25%
- Greater than 25%
Correct Answer: Greater than 25%
Q11. The Hall flowmeter funnel is primarily used to measure:
- Shear strength under consolidation
- Angle of repose
- Time required for a fixed mass of powder to flow through an orifice
- Electrostatic potential of powders
Correct Answer: Time required for a fixed mass of powder to flow through an orifice
Q12. Which particle shape favors the best powder flow?
- Irregular, plate-like
- Fibrous
- Spherical or near-spherical
- Angular, jagged
Correct Answer: Spherical or near-spherical
Q13. Moisture adsorption at low levels can sometimes improve flow by:
- Increasing electrostatic attraction
- Forming liquid bridges that increase cohesion
- Acting as a lubricant to reduce interparticle friction
- Creating hard agglomerates that block flow
Correct Answer: Acting as a lubricant to reduce interparticle friction
Q14. The major disadvantage of a high bulk density powder in filling operations is:
- Higher propensity to segregate
- More likely to produce light-weight tablets
- Smaller volume per unit mass, requiring different hopper design
- Always poorer flowability
Correct Answer: Smaller volume per unit mass, requiring different hopper design
Q15. Which property is NOT directly measured by tapped density apparatus?
- Tapped density value
- Compressibility (from bulk and tapped density)
- Shear strength under load
- Volume reduction on tapping
Correct Answer: Shear strength under load
Q16. Powder segregation during handling is most likely when:
- All particles are identical in size and density
- There is a broad particle size and density distribution
- The powder is fully granulated and coated
- The powder is cohesive and forms stable agglomerates
Correct Answer: There is a broad particle size and density distribution
Q17. Which test provides direct measurement of interparticle friction and cohesion under controlled normal stress?
- Angle of repose test
- Tapped density test
- Shear cell (Jenike) test
- Bulk density measurement
Correct Answer: Shear cell (Jenike) test
Q18. The flow function (ffc) classification indicating ‘free-flowing’ powders is approximately:
- ffc ≤ 1
- 1 < ffc < 2
- 4 < ffc < 10
- ffc > 100
Correct Answer: 4 < ffc < 10
Q19. Which of the following formulations strategies can reduce powder caking during storage?
- Increase humidity and store at high temperature
- Add glidants or anti-caking agents and control moisture
- Grind to produce more fines and enhance cohesion
- Remove all excipients
Correct Answer: Add glidants or anti-caking agents and control moisture
Q20. An increase in particle size generally has which effect on powder flow?
- Decreases flowability due to higher cohesion
- Increases flowability due to reduced surface area to volume ratio
- Always causes segregation in blends
- Has no effect on flow
Correct Answer: Increases flowability due to reduced surface area to volume ratio
Q21. What does a high Carr’s index (e.g., 30%) indicate about a powder?
- Excellent flowability and low compressibility
- High compressibility and poor flowability
- Very low tapped density only
- That the powder is free-flowing under all conditions
Correct Answer: High compressibility and poor flowability
Q22. Which excipient is commonly used as a glidant to improve powder flow?
- Lactose monohydrate
- Microcrystalline cellulose (MCC) in all cases
- Colloidal silicon dioxide (silica)
- Sucrose
Correct Answer: Colloidal silicon dioxide (silica)
Q23. Electrostatic charge in powders most commonly results in:
- Improved flow by reducing cohesion
- Increased adhesion to equipment and poor flow
- Reduction of bulk density only
- No observable effect in dry powders
Correct Answer: Increased adhesion to equipment and poor flow
Q24. Which property is directly calculated from mass and apparent volume of a poured powder?
- True density
- Bulk density
- Tapped density
- Flow function
Correct Answer: Bulk density
Q25. In pharmaceutical practice, why is powder flow important for tablet weight uniformity?
- Poor flow leads to variable die fill and weight variation
- Flow has no relation to die fill consistency
- Better flow always increases tablet disintegration time
- Flow only affects coated tablets
Correct Answer: Poor flow leads to variable die fill and weight variation
Q26. The Scott volumeter is used to measure:
- True density by gas pycnometry
- Bulk/tapped density under controlled aeration
- Bulk density using a known volume and vacuum-induced packing
- Angle of repose
Correct Answer: Bulk density using a known volume and vacuum-induced packing
Q27. Which change in process parameter is most likely to reduce powder segregation during blending?
- Increase blender speed to maximum
- Introduce an intermediate granulation step to reduce fines
- Dry the powder to extremely low humidity
- Decrease particle cohesion intentionally
Correct Answer: Introduce an intermediate granulation step to reduce fines
Q28. What does a low tapped-to-bulk density ratio (i.e., low Hausner ratio) indicate?
- High compressibility and very cohesive powder
- Low compressibility and good flow
- Extreme sensitivity to moisture
- High tendency to cake on storage
Correct Answer: Low compressibility and good flow
Q29. For inhalation powders, which flow property is especially critical?
- Very high bulk density irrespective of particle size
- Controlled aerodynamic particle size and good dispersibility
- Maximum electrical charge to stick to device
- Extremely high cohesiveness to prevent dispersion
Correct Answer: Controlled aerodynamic particle size and good dispersibility
Q30. Which approach is commonly used to quantify dynamic flow and wall friction for hopper design?
- Static angle of repose measurement only
- Ring shear tester or wall friction testing under consolidation
- Measuring true density by helium pycnometry only
- Determination of moisture sorption isotherm only
Correct Answer: Ring shear tester or wall friction testing under consolidation
I am a Registered Pharmacist under the Pharmacy Act, 1948, and the founder of PharmacyFreak.com. I hold a Bachelor of Pharmacy degree from Rungta College of Pharmaceutical Science and Research. With a strong academic foundation and practical knowledge, I am committed to providing accurate, easy-to-understand content to support pharmacy students and professionals. My aim is to make complex pharmaceutical concepts accessible and useful for real-world application.
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