Rotational viscometer MCQs With Answer

Rotational viscometer MCQs With Answer

Rotational viscometer MCQs with answer are essential for B.Pharm students studying viscosity measurement, rheology, and pharmaceutical formulations. This concise, SEO-friendly introduction covers key concepts like rotational viscometer types (Brookfield, cone-and-plate, cup-and-bob), torque, shear rate, Newtonian vs non-Newtonian behavior, temperature control, calibration, and application in suspensions, emulsions, and semisolids. These MCQs focus on practical laboratory considerations—spindle selection, sample volume, cleaning, and common errors—plus theory such as Ostwald-de Waele models, yield stress, and units (cP, Pa·s). Improve exam readiness and QC understanding with targeted practice. Now let’s test your knowledge with 50 MCQs on this topic.

Q1. What physical property does a rotational viscometer directly measure?

• Shear stress or torque related to fluid resistance
• Density of the fluid
• Surface tension
• Boiling point

Correct Answer: Shear stress or torque related to fluid resistance

Q2. Which instrument type is commonly referred to when students say “Brookfield viscometer”?

• Cone-and-plate viscometer
• Rotational spindle viscometer
• Capillary viscometer
• Falling-ball viscometer

Correct Answer: Rotational spindle viscometer

Q3. In rotational viscometry, torque is produced by:

• Gravitational forces on the spindle
• Viscous drag between spindle and sample
• Electrical current applied to the motor
• Ambient air flow

Correct Answer: Viscous drag between spindle and sample

Q4. Which property distinguishes Newtonian from non-Newtonian fluids in rotational measurements?

• Density dependence on temperature
• Viscosity independent of shear rate
• Viscosity varying with pH
• Color change under shear

Correct Answer: Viscosity independent of shear rate

Q5. Which spindle geometry generates a well-defined shear rate for low-viscosity fluids?

• Large cylindrical spindle
• Small cone-and-plate geometry
• Flat paddle in a large cup
• Irregular vane rotor

Correct Answer: Small cone-and-plate geometry

Q6. The SI unit of dynamic viscosity is:

• Poise (P)
• Centipoise (cP)
• Pascal-second (Pa·s)
• Newton (N)

Correct Answer: Pascal-second (Pa·s)

Q7. 1 centipoise (cP) equals how many Pa·s?

• 1 Pa·s
• 0.1 Pa·s
• 0.001 Pa·s
• 100 Pa·s

Correct Answer: 0.001 Pa·s

Q8. Which rheological model describes shear-thinning behavior commonly seen in polymer solutions?

• Bingham plastic model
• Newtonian model
• Ostwald-de Waele (power-law) model
• Hagen-Poiseuille model

Correct Answer: Ostwald-de Waele (power-law) model

Q9. A Bingham plastic fluid is characterized by:

• Viscosity decreasing with temperature only
• A yield stress that must be exceeded before flow
• Constant viscosity at all shear rates
• Zero viscosity at rest

Correct Answer: A yield stress that must be exceeded before flow

Q10. Which factor most strongly affects rotational viscometer readings for pharmaceutical suspensions?

• Ambient light intensity
• Particle size distribution and settling
• Electrical conductivity
• Color of the suspension

Correct Answer: Particle size distribution and settling

Q11. Why is temperature control critical during viscosity measurements?

• Temperature alters spindle geometry
• Viscosity is temperature-dependent and can change significantly
• To sterilize the sample during measurement
• To change the color of the sample

Correct Answer: Viscosity is temperature-dependent and can change significantly

Q12. In rotational viscometry, shear rate is primarily controlled by:

• Sample pH
• Rotational speed of the spindle
• Ambient humidity
• Duration of the measurement only

Correct Answer: Rotational speed of the spindle

Q13. Which error occurs if the spindle is not immersed to the recommended level?

• Increased electrical noise
• Incorrect torque reading due to air-sample interface effects
• Change in sample chemical composition
• Automatic calibration failure

Correct Answer: Incorrect torque reading due to air-sample interface effects

Q14. What is the typical use of a cone-and-plate viscometer in pharma labs?

• Measuring boiling points
• Precise shear rate control for low-volume samples and rheological characterization
• High-temperature viscosity of metals
• Measuring optical density

Correct Answer: Precise shear rate control for low-volume samples and rheological characterization

Q15. Which measurement indicates thixotropy in a sample?

• Viscosity increases with time under constant shear
• Viscosity decreases with time under constant shear and recovers on rest
• Viscosity is identical in up and down shear ramps
• No change in viscosity with time or shear

Correct Answer: Viscosity decreases with time under constant shear and recovers on rest

Q16. What is the role of calibration using viscosity standards?

• Set ambient room temperature
• Validate instrument accuracy across a range of viscosities
• Clean the spindle automatically
• Measure sample pH indirectly

Correct Answer: Validate instrument accuracy across a range of viscosities

Q17. Which rotor type is best for measuring high-viscosity gels and pastes?

• Small cone for low-viscosity fluids
• Vane or large cylindrical spindle
• Capillary tube
• Falling-sphere setup

Correct Answer: Vane or large cylindrical spindle

Q18. Torque limit on a viscometer indicates:

• Maximum allowable temperature
• Maximum torque the instrument can measure before overload
• Minimum sample volume needed
• Maximum spindle length

Correct Answer: Maximum torque the instrument can measure before overload

Q19. Which practice improves repeatability of viscosity measurements?

• Varying spindle speeds randomly
• Consistent spindle immersion depth, temperature, and equilibration time
• Using different spindles for each replicate
• Measuring at different room temperatures

Correct Answer: Consistent spindle immersion depth, temperature, and equilibration time

Q20. For non-Newtonian fluids, reporting viscosity at a given shear rate is important because:

• Viscosity is constant and independent of shear
• Viscosity varies with shear rate and context-specific values are meaningful
• Shear rate has no physical significance
• It helps determine color stability

Correct Answer: Viscosity varies with shear rate and context-specific values are meaningful

Q21. When measuring a shear-thinning suspension, increasing spindle speed typically results in:

• Higher measured viscosity
• Lower measured viscosity
• No change in viscosity
• Instrument failure

Correct Answer: Lower measured viscosity

Q22. What does the flow behavior index ‘n’ in the power-law model indicate when n<1?

• Shear-thickening (dilatant) behavior
• Shear-thinning (pseudoplastic) behavior
• Newtonian behavior
• Elastic solid behavior

Correct Answer: Shear-thinning (pseudoplastic) behavior

Q23. Which of the following is a common source of systematic error in rotational viscometry?

• Random electrical noise
• Incorrect spindle calibration factor
• Changes in operator handwriting
• Room lighting changes

Correct Answer: Incorrect spindle calibration factor

Q24. Cleaning spindles between samples is necessary because:

• It prevents cross-contamination and ensures accurate readings
• It increases spindle torque limit
• It calibrates the device automatically
• It changes the spindle geometry beneficially

Correct Answer: It prevents cross-contamination and ensures accurate readings

Q25. Which sample property can produce erratic torque readings due to wall slip?

• Highly adhesive, yield-stress fluids that slip at the rotor surface
• Completely Newtonian fluids
• Transparent solutions only
• Volatile solvents with low boiling points only

Correct Answer: Highly adhesive, yield-stress fluids that slip at the rotor surface

Q26. In quality control, why are viscosity specifications often given at a specific temperature and spindle speed?

• Because viscosity is independent of speed and temperature
• To ensure consistent, comparable measurements across batches
• To make testing slower
• To avoid measuring density

Correct Answer: To ensure consistent, comparable measurements across batches

Q27. Which viscometer type is preferred for very low viscosity liquids like water?

• Rotational spindle with large torque range only
• Cone-and-plate or capillary viscometer for precise low-viscosity measurements
• Vane spindle designed for heavy gels
• Manual cup-and-bob with no speed control

Correct Answer: Cone-and-plate or capillary viscometer for precise low-viscosity measurements

Q28. Dynamic viscosity relates shear stress to shear rate; kinematic viscosity equals dynamic viscosity divided by:

• Viscous index
• Density of the fluid
• Temperature in Kelvin
• Surface tension

Correct Answer: Density of the fluid

Q29. Which sample handling step reduces the effect of entrained air on viscosity readings?

• Shaking vigorously before testing
• Degassing or allowing time for entrained air to escape
• Heating to high temperatures above boiling point
• Adding surfactant immediately prior to test

Correct Answer: Degassing or allowing time for entrained air to escape

Q30. Which parameter is often plotted to determine yield stress from rotational viscometer data?

• Viscosity versus color
• Shear stress versus shear rate extrapolated to zero shear
• Temperature versus time
• Density versus spindle speed

Correct Answer: Shear stress versus shear rate extrapolated to zero shear

Q31. What is the effect of particle concentration on the apparent viscosity of suspensions?

• Higher particle concentration generally decreases apparent viscosity
• Higher particle concentration generally increases apparent viscosity
• Particle concentration has no effect
• It only affects color, not viscosity

Correct Answer: Higher particle concentration generally increases apparent viscosity

Q32. Which pharmaceutical formulation commonly requires rheological profiling by rotational viscometry?

• Parenteral aqueous solutions exclusively
• Topical creams, gels, suspensions, and syrups
• Solid tablets without lubrication
• Dry powders only

Correct Answer: Topical creams, gels, suspensions, and syrups

Q33. When validating a viscometer method, which attribute is NOT typically evaluated?

• Accuracy and precision
• Specificity for color measurement
• Linearity over the measurement range
• Stability and repeatability

Correct Answer: Specificity for color measurement

Q34. Which adjustment helps measure very low torques accurately?

• Use a higher viscosity sample
• Change to a more sensitive (low-torque) spindle/instrument range
• Increase spindle immersion arbitrarily
• Use a larger rotor designed for high torque

Correct Answer: Change to a more sensitive (low-torque) spindle/instrument range

Q35. What is the significance of the torque percentage reading on a rotational viscometer display?

• It indicates relative torque compared to the instrument’s full-scale range
• It measures sample density directly
• It shows battery life percentage
• It displays pH of the sample

Correct Answer: It indicates relative torque compared to the instrument’s full-scale range

Q36. In a rotational viscometer, increasing the gap between rotor and stator will generally:

• Increase measured shear rate for the same speed
• Decrease the shear rate experienced by the sample for the same speed
• Make the instrument measure surface tension
• Have no effect on measurement

Correct Answer: Decrease the shear rate experienced by the sample for the same speed

Q37. Which practice is recommended before switching between very different formulations on the same instrument?

• Change ambient light color
• Clean and, if needed, verify calibration to avoid cross-contamination
• Use the same spindle regardless of sample
• Increase motor speed to the maximum

Correct Answer: Clean and, if needed, verify calibration to avoid cross-contamination

Q38. Which morphologic sample change under shear is relevant to rheology of emulsions?

• Crystal melting only
• Droplet deformation and coalescence affecting viscosity
• Change in magnetic properties
• Change in refractive index only

Correct Answer: Droplet deformation and coalescence affecting viscosity

Q39. How is apparent viscosity reported for non-Newtonian fluids measured by rotational viscometers?

• As a single number independent of conditions
• As viscosity at a specified shear rate or spindle speed, often with shear-rate data
• Only as density equivalents
• Only as torque percentages

Correct Answer: As viscosity at a specified shear rate or spindle speed, often with shear-rate data

Q40. Which of the following is a benefit of automated rotation and data acquisition in viscometers?

• Increased variability between readings
• Improved consistency, programmable shear ramps, and data logging
• Reduced need for calibration ever
• Automatic sample heating to boiling

Correct Answer: Improved consistency, programmable shear ramps, and data logging

Q41. What is the likely consequence of measuring a volatile solvent without a sealed cup at elevated temperature?

• Improved viscosity accuracy
• Evaporation leading to concentration change and erroneous readings
• No change in results
• Automatic compensation by the viscometer

Correct Answer: Evaporation leading to concentration change and erroneous readings

Q42. Which mathematical transform is commonly used to linearize power-law rheology data?

• Log-log plot of shear stress versus shear rate
• Square root transform of temperature
• Reciprocal transform of viscosity only
• Exponential smoothing

Correct Answer: Log-log plot of shear stress versus shear rate

Q43. For thin polymer solutions, what rheological parameter helps characterize molecular interactions and entanglements?

• Yield point only
• Shear-thinning index and viscoelastic parameters from oscillatory tests
• Optical rotation
• Magnetic susceptibility

Correct Answer: Shear-thinning index and viscoelastic parameters from oscillatory tests

Q44. Which descriptive term applies to fluids whose viscosity increases with increasing shear rate?

• Pseudoplastic
• Dilatant (shear-thickening)
• Newtonian
• Bingham plastic

Correct Answer: Dilatant (shear-thickening)

Q45. When interpreting viscosity results for regulatory submissions, what is important to include?

• Room paint color during testing
• Detailed method: instrument model, spindle, speed(s), temperature, equilibration time
• Only the brand of the viscometer without parameters
• Operator favorite settings without specifics

Correct Answer: Detailed method: instrument model, spindle, speed(s), temperature, equilibration time

Q46. What is the correct response if a sample produces torque readings at or above instrument full-scale?

• Proceed and report the full-scale reading
• Switch to a higher torque range spindle or instrument to avoid overload
• Reduce sample temperature to freeze it
• Increase spindle speed further

Correct Answer: Switch to a higher torque range spindle or instrument to avoid overload

Q47. Which parameter obtained from rotational viscometry helps in predicting syringeability of parenteral formulations?

• Electrical resistance
• Viscosity at relevant shear rates and yield stress
• Boiling point
• Color intensity

Correct Answer: Viscosity at relevant shear rates and yield stress

Q48. What is the main advantage of using a cup-and-bob (Couette) geometry?

• Simple visual observation only
• Uniform shear conditions and good control for suspensions and high-viscosity samples
• It measures thermal conductivity
• No need for calibration

Correct Answer: Uniform shear conditions and good control for suspensions and high-viscosity samples

Q49. Which factor can falsely lower measured viscosity due to sample heating during measurement?

• Using an insulated cup
• High spindle speed generating viscous heating in concentrated samples
• Performing the test at low ambient temperature
• Using a larger sample volume

Correct Answer: High spindle speed generating viscous heating in concentrated samples

Q50. How can one determine if wall slip is affecting a viscometer measurement?

• Compare viscosity results using different surface roughness rotors or gap sizes; if values change significantly, wall slip may be present
• Only by measuring color changes
• By measuring pH simultaneously
• By decreasing temperature to freezing point

Correct Answer: Compare viscosity results using different surface roughness rotors or gap sizes; if values change significantly, wall slip may be present

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