Introduction: The Law of Flow MCQs With Answer is a focused study resource for B. Pharm students studying powder and granular flow in pharmaceutics. This introduction covers flow principles, measurement methods, practical equations and factors affecting powder flowability, such as particle size, shape, humidity, and excipients like glidants and lubricants. Key terms include angle of repose, Carr’s index, Hausner ratio, bulk/tapped density, Beverloo and Darcy relations, and Jenike theory—essential for formulation, granulation, tablet die filling and scale-up. Clear understanding of these laws helps prevent issues like bridging, rat-holing and segregation during manufacturing. Now let’s test your knowledge with 50 MCQs on this topic.
Q1. What does Carr’s compressibility index indicate about a powder?
- It quantifies flowability; lower values indicate better flow
- It measures chemical stability of the powder
- It indicates moisture content only
- It determines particle charge
Correct Answer: It quantifies flowability; lower values indicate better flow
Q2. How is Hausner ratio calculated?
- Bulk density divided by tapped density
- Tapped density divided by bulk density
- True density divided by bulk density
- Tapped density minus bulk density
Correct Answer: Tapped density divided by bulk density
Q3. Which of the following best describes angle of repose?
- The maximum static slope angle of a piled powder
- The contact angle between powder and water
- The friction angle of tablet punches
- The angle of a tablet bevel
Correct Answer: The maximum static slope angle of a piled powder
Q4. Which equation gives terminal settling velocity of small spherical particles in a viscous fluid?
- Darcy’s law
- Stokes’ law
- Beverloo equation
- Hagen-Poiseuille equation
Correct Answer: Stokes’ law
Q5. What does a Hausner ratio greater than 1.25 generally indicate?
- Excellent flowability
- Moderate to poor flowability
- High true density
- Low moisture sensitivity
Correct Answer: Moderate to poor flowability
Q6. Which method is commonly used to measure tapped density?
- Pycnometer
- Tap-tester apparatus that taps a graduated cylinder
- Angle of repose cone method
- Laser diffraction
Correct Answer: Tap-tester apparatus that taps a graduated cylinder
Q7. Beverloo’s equation is used to predict which powder property?
- Mass flow rate through an orifice
- Bulk density under vibration
- Angle of repose
- True particle density
Correct Answer: Mass flow rate through an orifice
Q8. Which factor most directly reduces powder cohesion and improves flow when added in small amounts?
- Glidant like colloidal silicon dioxide
- Plasticizer like PEG
- Bulk filler like lactose
- Disintegrant like croscarmellose
Correct Answer: Glidant like colloidal silicon dioxide
Q9. What is the physical meaning of bulk density?
- Mass per unit volume of powder including inter-particle voids
- Mass per unit volume of individual particles excluding voids
- Mass per unit volume of liquid in a suspension
- Surface area per unit mass
Correct Answer: Mass per unit volume of powder including inter-particle voids
Q10. Which instrument directly measures powder shear properties and flow function?
- Angle of repose apparatus
- Powder shear cell
- Tapped density tester
- Laser diffraction particle sizer
Correct Answer: Powder shear cell
Q11. Which of the following reduces powder flowability?
- Increasing particle size (for non-cohesive powders)
- Spherical particle shape
- High humidity causing liquid bridges
- Addition of colloidal silica in trace amounts
Correct Answer: High humidity causing liquid bridges
Q12. Darcy’s law relates to which type of flow relevant in pharmaceutics?
- Flow of Newtonian liquids in capillaries only
- Flow of air through porous powder beds
- Flow of molten polymers
- Gas chromatographic separation
Correct Answer: Flow of air through porous powder beds
Q13. Which parameter is primarily used to evaluate flow improvement after granulation?
- Decrease in true density
- Increase in particle size and improved Carr’s index
- Change in color
- Reduction in melting point
Correct Answer: Increase in particle size and improved Carr’s index
Q14. What does ‘mass flow’ in a hopper imply?
- Only central core flows while walls are stagnant
- All powder moves uniformly toward the outlet
- Complete adhesion to hopper walls
- Flow only under vibration
Correct Answer: All powder moves uniformly toward the outlet
Q15. Which of the following is a sign of poor flow during tablet compression?
- Uniform tablet weight
- Frequent weight variation and tablet weight loss
- Smooth punch faces
- Low ejection force
Correct Answer: Frequent weight variation and tablet weight loss
Q16. Which packing property is most relevant to powder compressibility?
- True density
- Porosity and bulk/tapped density relationship
- Optical density
- Thermal conductivity
Correct Answer: Porosity and bulk/tapped density relationship
Q17. Which of the following best reduces segregation during blending?
- Using highly different particle sizes
- Using granulation or particle size reduction to narrow distribution
- Adding moisture to form hard lumps
- Increasing blending speed indefinitely
Correct Answer: Using granulation or particle size reduction to narrow distribution
Q18. What is a common effect of magnesium stearate when over-mixed with powder blends?
- Increased dissolution due to improved wettability
- Hydrophobic coating causing reduced tablet tensile strength and dissolution
- Increased bulk density dramatically
- Conversion to crystalline API
Correct Answer: Hydrophobic coating causing reduced tablet tensile strength and dissolution
Q19. Which measurement technique gives particle size distribution important for flow behavior?
- Powder shear cell
- Laser diffraction particle sizing
- Tapped density test
- Loss on drying
Correct Answer: Laser diffraction particle sizing
Q20. What causes ‘bridging’ in hoppers?
- Very small outlet diameter relative to particle size and cohesion
- Excessively large outlet diameter
- Use of glidants
- Complete fluidization
Correct Answer: Very small outlet diameter relative to particle size and cohesion
Q21. Which property is measured by a pycnometer in powder characterization?
- Bulk density
- True (particle) density
- Angle of repose
- Flow rate through orifice
Correct Answer: True (particle) density
Q22. For a conical pile of powder with height h and base diameter D, which relation gives tan θ (angle of repose)?
- tan θ = h/D
- tan θ = 2h/D
- tan θ = D/2h
- tan θ = h^2/D
Correct Answer: tan θ = 2h/D
Q23. What is the main reason roller compaction can improve flow of a powder?
- It decreases particle size dramatically
- It produces granules with increased density and size improving flow
- It dissolves the powder
- It increases surface charge to reduce cohesion
Correct Answer: It produces granules with increased density and size improving flow
Q24. Which flow behavior is most associated with cohesive fine powders?
- Free-flowing with low cohesion
- High tendency to form agglomerates, bridge and rat-hole
- Immediate complete fluidization at low air flow
- High pourability even at high humidity
Correct Answer: High tendency to form agglomerates, bridge and rat-hole
Q25. Which parameter improves when a powder is treated with colloidal silica?
- Chemical potency
- Flowability by reducing interparticle friction
- True density significantly
- Melting point
Correct Answer: Flowability by reducing interparticle friction
Q26. Which of these is NOT typically a direct cause of poor flow?
- Irregular particle shape
- Electrostatic charge
- Low moisture creating brittle particles
- High specific surface area
Correct Answer: Low moisture creating brittle particles
Q27. The flow function obtained from a shear cell is primarily used for what?
- Predicting granule dissolution
- Designing hopper outlet size and angle to ensure mass flow
- Determining API purity
- Assessing color stability
Correct Answer: Designing hopper outlet size and angle to ensure mass flow
Q28. Which of the following increases powder flow under vibration?
- Increased cohesion due to moisture
- Particle interlocking
- Mobilization of particles reducing friction at contacts
- Formation of hard lumps
Correct Answer: Mobilization of particles reducing friction at contacts
Q29. Which term describes the fraction of void space in a powder bed?
- Porosity
- Tortuosity
- Viscosity
- Surface energy
Correct Answer: Porosity
Q30. Which instrument best quantifies dynamic flow behavior of powders during processing?
- Tablet hardness tester
- Powder rheometer
- Tapped density tester only
- UV-Vis spectrophotometer
Correct Answer: Powder rheometer
Q31. In Beverloo’s equation, increasing the orifice diameter D primarily does what to mass flow rate?
- Decreases flow rate
- Increases flow rate strongly (approx. D^{5/2})
- Has no effect
- Only affects particle shape
Correct Answer: Increases flow rate strongly (approx. D^{5/2})
Q32. Which of the following is a common threshold for angle of repose indicating good flow?
- Greater than 50°
- Less than 30°
- Exactly 45° only
- Between 40° and 60°
Correct Answer: Less than 30°
Q33. What is rat-holing in powder flow?
- Entire powder mass flows uniformly
- A narrow flow channel forms while material near walls remains stagnant
- Powder dissolves in exit air
- Powder becomes electrically charged
Correct Answer: A narrow flow channel forms while material near walls remains stagnant
Q34. Which powder property is most likely to change after wet granulation?
- True density of the API
- Particle size distribution and bulk/tapped density
- Chemical structure of API
- Melting point
Correct Answer: Particle size distribution and bulk/tapped density
Q35. Which of the following is an effect of electrostatic charging on powders?
- Improved flow due to reduced adhesion
- Increased cohesion and adhesion to equipment walls causing poor flow
- Neutral effect on flow always
- Instant dissolution in humidity
Correct Answer: Increased cohesion and adhesion to equipment walls causing poor flow
Q36. For powders, what does a lower Carr’s index value signify in numeric terms?
- Higher compressibility
- Lower compressibility and better flow
- Higher moisture content only
- Lower true density always
Correct Answer: Lower compressibility and better flow
Q37. Which processing step often reduces segregation in blended powders?
- Dry sieving to produce a wider size distribution
- Granulation to form larger, uniform agglomerates
- Adding volatile solvents
- Increasing static charge
Correct Answer: Granulation to form larger, uniform agglomerates
Q38. Which surface characteristic increases interparticle friction and reduces flow?
- Smooth spherical surfaces
- Rough, angular particle surfaces
- Lubricant coating
- Use of glidants
Correct Answer: Rough, angular particle surfaces
Q39. Which unit is typically used for bulk density in pharmaceutical contexts?
- g/cm3 or g/mL
- kg/mol
- Pascal
- m2/s
Correct Answer: g/cm3 or g/mL
Q40. What is the main advantage of using granules over fine powders in tablet production?
- Granules are harder to compress
- Improved flowability and more uniform die filling
- Lower drug content uniformity
- Higher hygroscopicity always
Correct Answer: Improved flowability and more uniform die filling
Q41. Which of the following increases as powder porosity decreases?
- Bulk volume for same mass
- Bulk density
- Inter-particle voids
- Flow rate always decreases
Correct Answer: Bulk density
Q42. Which parameter is NOT directly part of Stokes’ law for terminal velocity?
- Particle radius
- Viscosity of medium
- Particle temperature
- Density difference between particle and fluid
Correct Answer: Particle temperature
Q43. Which action is recommended to reduce bridging in a hopper?
- Reduce outlet diameter
- Use hopper inserts or increase outlet size and wall slope
- Increase powder cohesion intentionally
- Cool the powder drastically
Correct Answer: Use hopper inserts or increase outlet size and wall slope
Q44. Which phenomenon can cause fines to elutriate and segregate during pneumatic transfer?
- Insufficient air velocity
- Excessive cohesion only
- High air velocity causing entrainment of fines
- Use of glidants
Correct Answer: High air velocity causing entrainment of fines
Q45. Which of these best characterizes flow in a ‘funnel flow’ hopper?
- All material moves uniformly toward the outlet
- Only a central channel flows while material near walls remains stationary
- Material flows only when heated
- Material never flows
Correct Answer: Only a central channel flows while material near walls remains stationary
Q46. What effect does narrowing particle size distribution usually have on powder flow?
- Increases segregation
- Generally improves flow and reduces segregation
- Always makes flow poorer
- Has no effect on flow
Correct Answer: Generally improves flow and reduces segregation
Q47. Which additive is commonly used as a glidant to enhance powder flow?
- Sodium chloride
- Colloidal silicon dioxide (Aerosil)
- Hydroxypropyl methylcellulose
- Ascorbic acid
Correct Answer: Colloidal silicon dioxide (Aerosil)
Q48. Which property measured by tapped and bulk density tests is critical for capsule filling and die filling consistency?
- Optical clarity
- Compressibility index (Carr’s index) and Hausner ratio
- Boiling point
- Melting point
Correct Answer: Compressibility index (Carr’s index) and Hausner ratio
Q49. Which of the following strategies can reduce electrostatic problems in powder handling?
- Increase relative humidity and use proper grounding or antistatic measures
- Decrease humidity to zero always
- Use only metallic powders
- Coat particles with hydrophobic materials
Correct Answer: Increase relative humidity and use proper grounding or antistatic measures
Q50. Why is understanding flow laws essential during scale-up of tablet manufacturing?
- Flow laws only affect color uniformity
- They help predict hopper design, die filling, segregation risk and consistent tablet weight at larger scales
- Scale-up does not change flow behavior
- They are only relevant for liquid formulations
Correct Answer: They help predict hopper design, die filling, segregation risk and consistent tablet weight at larger scales
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