Viscosity determination methods MCQs With Answer

Viscosity determination methods MCQs With Answer

Understanding viscosity determination methods is essential for B.Pharm students involved in formulation, quality control, and rheological analysis of pharmaceutical products. This concise, informative introduction covers capillary viscometers (Ostwald, Ubbelohde), rotational viscometers (Brookfield), falling ball and Stokes’ law approaches, kinematic vs dynamic viscosity, and rheological behavior of Newtonian and non-Newtonian fluids. Emphasis is placed on calibration, units (Pa·s, cP), temperature dependence, intrinsic viscosity, and polymer solution viscometry methods relevant to drugs, syrups, suspensions, and ointments. Master these concepts to select appropriate viscometry techniques for pharmaceutical formulations. Now let’s test your knowledge with 50 MCQs on this topic.

Q1. Which viscometer is based on measuring the time for a liquid to flow through a capillary under gravity?

• Rotational viscometer
• Ostwald capillary viscometer
• Falling ball viscometer
• Brookfield cone-and-plate viscometer

Correct Answer: Ostwald capillary viscometer

Q2. Dynamic viscosity is defined as the ratio of shear stress to what other parameter?

• Shear strain
• Viscous torque
• Shear rate
• Shear modulus

Correct Answer: Shear rate

Q3. Kinematic viscosity equals dynamic viscosity divided by which physical property?

• Density
• Surface tension
• Viscometer constant
• Temperature

Correct Answer: Density

Q4. Which instrument is best suited for measuring viscosity of non-Newtonian, shear-thinning creams?

• Ostwald capillary viscometer
• Falling ball viscometer
• Rotational rheometer (cone-and-plate)
• Ubbelohde viscometer

Correct Answer: Rotational rheometer (cone-and-plate)

Q5. In falling ball viscometry, viscosity is calculated using terminal velocity and which law?

• Poiseuille’s law
• Stokes’ law
• Hagen-Poiseuille equation
• Newton’s law of cooling

Correct Answer: Stokes’ law

Q6. The Ubbelohde viscometer differs from Ostwald primarily because it:

• Is used only for non-Newtonian fluids
• Has a suspended reservoir to eliminate hydrostatic head differences
• Measures shear stress directly
• Uses a falling ball mechanism

Correct Answer: Has a suspended reservoir to eliminate hydrostatic head differences

Q7. Which unit is commonly used for dynamic viscosity in the CGS system?

• Pascal-second (Pa·s)
• Centipoise (cP)
• Stokes (St)
• Poise (P)

Correct Answer: Poise (P)

Q8. Relative viscosity (η_rel) of a polymer solution is defined as the ratio of:

• Viscosity of solvent to viscosity of solution
• Viscosity of solution to viscosity of solvent
• Intrinsic viscosity to reduced viscosity
• Viscosity at two different temperatures

Correct Answer: Viscosity of solution to viscosity of solvent

Q9. Intrinsic viscosity [η] provides information about:

• Solvent evaporation rate
• Molecular weight and shape of polymers
• Surface tension of formulations
• Thermal conductivity

Correct Answer: Molecular weight and shape of polymers

Q10. The Huggins equation relates reduced viscosity to concentration and yields which constant when extrapolated to zero concentration?

• Huggins constant (kH)
• Intrinsic viscosity [η]
• Mark–Houwink exponent (a)
• Viscosity index

Correct Answer: Intrinsic viscosity [η]

Q11. Which relation describes temperature dependence of viscosity for many liquids using an exponential form?

• Arrhenius equation
• Mark–Houwink equation
• Huggins equation
• Stokes’ law

Correct Answer: Arrhenius equation

Q12. Brookfield viscometers primarily measure viscosity by recording:

• Time for capillary flow
• Torque required to rotate a spindle at a set speed
• Terminal velocity of a sphere
• Oscillation frequency of a probe

Correct Answer: Torque required to rotate a spindle at a set speed

Q13. A shear-thinning fluid exhibits what behavior as shear rate increases?

• Viscosity increases
• Viscosity remains constant
• Viscosity decreases
• Viscosity oscillates

Correct Answer: Viscosity decreases

Q14. Which parameter describes the sensitivity of viscosity to temperature changes for lubricants and oils?

• Viscosity index
• Huggins constant
• Intrinsic viscosity
• Reynolds number

Correct Answer: Viscosity index

Q15. For polymer solutions, the Mark–Houwink equation relates intrinsic viscosity to:

• Solubility parameter
• Molecular weight
• Glass transition temperature
• Surface tension

Correct Answer: Molecular weight

Q16. Which viscometer principle measures resistance to flow between two surfaces, one rotating and one stationary?

• Capillary viscometer
• Falling ball viscometer
• Couette (rotational) viscometer
• Stroboscopic viscometer

Correct Answer: Couette (rotational) viscometer

Q17. In capillary viscometry, the viscometer constant is determined by:

• Measuring density only
• Calibration with a standard liquid of known viscosity
• Measuring surface tension
• Measuring temperature at two points

Correct Answer: Calibration with a standard liquid of known viscosity

Q18. Which factor has the largest influence on viscosity measurements if not properly controlled?

• Color of the sample
• Temperature
• Ambient light
• Container shape

Correct Answer: Temperature

Q19. Newtonian fluids are characterized by:

• Viscosity changes with shear rate
• Elastic behavior under stress
• Constant viscosity independent of shear rate
• Time-dependent viscosity only

Correct Answer: Constant viscosity independent of shear rate

Q20. The reduced viscosity (η_red) is calculated as (η_rel – 1)/c. What does η_rel represent?

• Viscosity of solvent divided by solution viscosity
• Viscosity of solution divided by viscosity of solvent
• Intrinsic viscosity times concentration
• Huggins constant times concentration

Correct Answer: Viscosity of solution divided by viscosity of solvent

Q21. Viscosity measurement of suspensions can be complicated by:

• Uniform particle size and no interactions
• Particle settling, thixotropy and shear-induced structuring
• Constant viscosity with shear
• Absence of Brownian motion

Correct Answer: Particle settling, thixotropy and shear-induced structuring

Q22. Andrade’s equation is used to describe viscosity dependence on:

• Pressure
• Temperature
• Concentration only
• Shear rate

Correct Answer: Temperature

Q23. Which of the following is a measure of fluid’s resistance to flow under applied stress in dynamic terms?

• Kinematic viscosity
• Dynamic (absolute) viscosity
• Surface tension
• Specific gravity

Correct Answer: Dynamic (absolute) viscosity

Q24. When using an Ostwald viscometer, cleaning and drying between samples is important because residues can:

• Decrease solvent density only
• Alter capillary dimensions and affect flow time
• Change atmospheric pressure drastically
• Have no effect on measurement

Correct Answer: Alter capillary dimensions and affect flow time

Q25. Which rheological behavior shows time-dependent recovery of viscosity after shear is removed?

• Newtonian behavior
• Thixotropy
• Rheopecty
• Shear-thinning instantaneous

Correct Answer: Thixotropy

Q26. A sample showing increasing viscosity with time under constant shear is called:

• Thixotropic
• Shear-thinning
• Rheopectic
• Newtonian

Correct Answer: Rheopectic

Q27. In capillary viscometry, the Hagen–Poiseuille equation relates flow rate to viscosity and which other parameter?

• Surface roughness
• Capillary radius and pressure drop
• Color of fluid
• Evaporation rate

Correct Answer: Capillary radius and pressure drop

Q28. Which standard condition is most often specified for viscosity measurements?

• Constant humidity only
• Specified temperature (e.g., 25 °C or 20 °C)
• Specific light intensity
• Complete vacuum

Correct Answer: Specified temperature (e.g., 25 °C or 20 °C)

Q29. For dilute polymer solutions, intrinsic viscosity is found by extrapolating which plot to zero concentration?

• Viscosity vs. temperature
• Reduced viscosity or inherent viscosity vs. concentration
• Density vs. concentration
• Viscosity vs. shear rate

Correct Answer: Reduced viscosity or inherent viscosity vs. concentration

Q30. The Mark–Houwink equation has the form [η] = K·M^a. The exponent ‘a’ gives information about:

• Polymer molecular weight distribution
• Molecular conformation in solution (coil/rod)
• Temperature sensitivity
• Surface activity

Correct Answer: Molecular conformation in solution (coil/rod)

Q31. Which factor must be corrected for when comparing viscosity measurements at different altitudes?

• Surface tension
• Atmospheric pressure influence on capillary flow
• Color of the sample
• Electrical conductivity

Correct Answer: Atmospheric pressure influence on capillary flow

Q32. In viscometry, the term “shear stress” is defined as force per unit area acting parallel to the surface. Its SI unit is:

• Pascal (Pa)
• Newton-meter (N·m)
• Pascal-second (Pa·s)
• Poise (P)

Correct Answer: Pascal (Pa)

Q33. The Cox–Merz rule is an empirical correlation between steady shear viscosity and:

• Oscillatory complex viscosity vs frequency
• Thermal conductivity
• Intrinsic viscosity vs concentration
• Density vs temperature

Correct Answer: Oscillatory complex viscosity vs frequency

Q34. Which viscometer is most suitable to measure very low viscosities (e.g., gases or low-viscosity liquids)?

• Falling ball viscometer
• Cannon–Fenske viscometer for kinematic viscosity
• Brookfield spindle at low speed
• Rotational cone-and-plate for high-viscosity gels

Correct Answer: Cannon–Fenske viscometer for kinematic viscosity

Q35. Which of the following is a common source of error in rotational viscometer measurements?

• Using a perfectly clean spindle
• Inadequate sample volume leading to end effects
• Constant temperature control
• Proper spindle alignment

Correct Answer: Inadequate sample volume leading to end effects

Q36. The term “apparent viscosity” is used mainly for:

• Newtonian fluids only
• Liquids with color additives
• Non-Newtonian fluids at a specified shear rate
• Gases under high pressure

Correct Answer: Non-Newtonian fluids at a specified shear rate

Q37. When determining intrinsic viscosity of a polymer, selection of solvent should ensure:

• Solvent is non-volatile only
• Polymer is fully dissolved and behaves ideally at dilute concentrations
• High ionic strength to stabilize particles
• Solvent density equals polymer density

Correct Answer: Polymer is fully dissolved and behaves ideally at dilute concentrations

Q38. Which calibration practice is essential for capillary viscometers?

• Never calibrate if using distilled water
• Regular calibration with standard liquids of known viscosity at test temperature
• Calibrate only once after purchase
• Calibration by comparing colors

Correct Answer: Regular calibration with standard liquids of known viscosity at test temperature

Q39. For pharmaceutical syrups, viscosity affects which critical property?

• pH stability only
• Pourability, mouthfeel and drug release
• Color retention
• Electrical conductivity

Correct Answer: Pourability, mouthfeel and drug release

Q40. Viscosity measurements required for quality control should follow:

• Manufacturer’s recipe only
• Recognized standards (e.g., USP, ISO) and validated methods
• Random measurement procedures
• Only visual inspection

Correct Answer: Recognized standards (e.g., USP, ISO) and validated methods

Q41. In viscometry, Reynolds number helps to determine whether flow is:

• Laminar or turbulent
• Newtonian or non-Newtonian
• Compressible or incompressible
• Viscous or inviscid

Correct Answer: Laminar or turbulent

Q42. A polymer solution with high intrinsic viscosity likely indicates:

• Low molecular weight polymer
• High molecular weight or expanded coil conformation
• Solvent incompatibility
• Low polymer concentration

Correct Answer: High molecular weight or expanded coil conformation

Q43. Which method measures viscosity by observing the time a fixed volume takes to pass between marks under gravity?

• Brookfield viscometer
• Capillary viscometry (Ostwald/Ubbelohde)
• Falling sphere method
• Rotational shear rheometry

Correct Answer: Capillary viscometry (Ostwald/Ubbelohde)

Q44. Surface active agents (surfactants) in a formulation can affect viscosity mainly by:

• Changing molecular weight of solvent
• Altering intermolecular interactions and micelle formation
• Increasing atmospheric pressure
• Reducing temperature sensitivity

Correct Answer: Altering intermolecular interactions and micelle formation

Q45. Which viscosity parameter is typically reported for oils in the petroleum industry at 40 °C?

• Intrinsic viscosity
• Kinematic viscosity in cSt (centistokes)
• Surface tension in mN/m
• Dynamic viscosity in P only

Correct Answer: Kinematic viscosity in cSt (centistokes)

Q46. The presence of dissolved gases or air bubbles in a sample generally causes viscosity measurements to:

• Be more accurate
• Remain unchanged
• Be erroneous due to lower apparent viscosity and noise
• Show higher intrinsic viscosity

Correct Answer: Be erroneous due to lower apparent viscosity and noise

Q47. Which approach is most appropriate to measure yield stress and flow curve of a paste-like pharmaceutical ointment?

• Ostwald viscometer
• Rotational rheometry with controlled stress/strain tests
• Falling ball viscometer
• Simple settling test

Correct Answer: Rotational rheometry with controlled stress/strain tests

Q48. When using a rotational viscometer, increasing spindle speed will generally:

• Always increase measured viscosity for any fluid
• Have no effect on Newtonian fluids but may change apparent viscosity for non-Newtonian fluids
• Reduce density of the sample
• Change the chemical composition

Correct Answer: Have no effect on Newtonian fluids but may change apparent viscosity for non-Newtonian fluids

Q49. The primary advantage of capillary viscometers is:

• Ability to measure high-viscosity pastes directly
• Simplicity, reproducibility and suitability for low-viscosity Newtonian liquids
• Direct measurement of yield stress
• Measuring viscoelastic moduli

Correct Answer: Simplicity, reproducibility and suitability for low-viscosity Newtonian liquids

Q50. During viscosity method selection for a pharmaceutical dosage form, the most important considerations include:

• Color and odor of the product only
• Rheological behavior (Newtonian vs non-Newtonian), sample volume, temperature control and measurement range
• Brand of equipment only
• Whether the sample is solid at room temperature only

Correct Answer: Rheological behavior (Newtonian vs non-Newtonian), sample volume, temperature control and measurement range

G S Sachin

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.

Mail- Sachin@pharmacyfreak.com